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MG TD TF 1500 - Alternator Electrical Question

I have installed an alternator to replace the generator and regulator. It is from a company in England called Accuspark. They call it a Dynamator and it is built in the body of the standard TD generator. The car is running fine but my ammeter is erratic. This is an email I wrote to them:

The Dynamator is installed and working.
I have a question for you. Since installing the Dynamator I have noticed that my ammeter is very erratic. It has been suggested to me that my ammeter was designed for the original generator/regulator and that the Dynamator has very different electrical characteristics.
Attached is a photograph of my ammeter. I believe it is the original or at least a period correct instrument.
Is there anyway to modify this ammeter for better performance with your Dynamator?
Alternatively might you know where I could obtain a replacement that would look and perform correctly?
Thank you,
Mort Resnicoff

This is their reply:

Sorry canít really offer any specific answer , broadly you unit is not really suitable and we not really recommend using it as is . It should be converted to handle much higher amps . Ideally it should be converted to a volt meter .

I would appreciate any thoughts on this issue.


Mort Resnicoff

I think they are right. How many amps does the new deal put out? I'm guessing a lot more than 20,which if wired to go through the original ammeter, will burn or melt it. Most all of the replacement ammeters of new and old manufacture have a 60A capacity, and have black/white dials and letters. George
George Butz III

Mort, can you describe the ammeter's actions with a bit more detail? The 20 amp meter should survive the output of the alternator unless you have a virtually dead battery that it's trying to charge. Where is the wire from the ammeter that used to go to terminal A of the Control Box (regulator) now connected? I'm assuming that the other side of the ammeter is still connected to the battery lead. I'll see if I can find Accuspark's directions. Bud
Bud Krueger

I have a TF (negative earth) with a Dynamator and the 30A ammeter is steady, showing very little deflection. I would expect more movement on your 20A ammeter but would be surprised if you ever get a full meter deflection. Provided that is the case and your ammeter is in good working order, there should not be an issue. However if you haven't done so, you should upgrade the wiring to the ammeter and battery.
The comment from Accuspark about using a voltmeter instead is valid as its more useful and definitely more safe to do so. Why? Voltmeters are high resistance devices that pass very little current and are therefore safer. The prospect of 40A flowing up to the dash and back safely is not a good one. This is one reason why modern cars with very highly rated ammeters have voltmeters, if they have anything at all. The problem with fitting a traditional Voltmeter for some is that its highly visible and non original. I got around this by fitting a very small colour changing Voltage sensitive LED. These are sold specifically for this application by outfits like Gammatronix. Such an led can be mounted unobtrusively under the dash or by the steering column, etc., and tell you all you need to know. I left the ammeter connected, but it would be wiser to bypass it.
Dave H
Dave Hill

From Google: Accuspark's wiring diagram shows its connection to an RB106 (5 terminal) regulator. The ONLY terminal used is E, the ground terminal. No ammeter is shown in the diagram. The ammeter in our cars needs to be looked at as showing current into (+) or out of (-) the battery. The wiring directions that I've seen so far leave much to be desired. Telling the owner to install a heavy gauge wire to the ammeter, without telling him where and how to connect the other side of the ammeter doesn't help. Bud
Bud Krueger

My view is that its better to make comments or give advice in reasonable sized chunks, so that if more information is required, they can ask for it. Otherwise we end up with long parables on here that the guy already knows and bores the pants off everyone else.
Dave H
Dave Hill

You're right, Dave. Would anyone care to share a copy of the supplier's installation instructions?

Last week I came within a whisker of asking Santa for a Dynamator for Christmas. I'm looking for more current at idling speeds during parades. Bud
Bud Krueger

I installed the same alternator in my race TD earlier this year. Modified the regulator into a dummy terminal box and everything works as it should including the original ammeter and warning light.

F Filangeri

I did the same, but I agree the instructions provided with the Dynamator were insufficient. However, some searching on the net and you can find all you need. Most useful were the wiring diagrams provided with the Dynalite alternator (a more expensive alternative). I'm not sure they are still on their website.
Dave H
Dave Hill

This link shows the wiring for a modified RB106 compatible with the alternators. Completely gut an old regulator removing the coils and resistor underneath and connect as shown in the "after" diagram. Fuse optional but recommended.

F Filangeri

Thanks Frank. The link leads me to a '404 Error', but it gives me enough links to find the diagrams for Dynalite stuff.
None of the diagrams that I can find show the wiring for an ammeter. The dummy RB106 is only being used for the sake of connecting wires together at the A terminal. That's one side of the ammeter. But, the battery's also connected to that terminal. And, that's the other side of the ammeter.

I hate to be a pest, but I'd like to help Mort solve his problem. I'm hoping to find someone who can tell me where his ammeter is connected in a working Dynamater. Mort's workmanship is outstanding. Bud
Bud Krueger

Try this link and scroll down to the "dummy regulator" diagram. If the ammeter worked before it should work after installing the dummy regulator. No change to ammeter wiring is required. Installed a simlar unit on my XKE and it worked there as well with everything functioning normally.
F Filangeri


You did rewire it eliminating the old regulator, right? Might be the DC regulator cutting in & out if it is still hooked up.

I stuck one in a year or so ago and it took quite a bit of headscratching to understand:
1: Why it didn't start charging after starting the engine;
2: How much resistance to add for the field lead since there were no instructions nor explanations;
3: Why it appears to stop charging at idle like the old generator.

It seems the field needs at least 12.0V or so to get it charging. If there is NO feed to the field terminal, no wire whatsoever, it MAY activate itself when it is revved up, it depends on the battery voltage. But don't count on it! IF battery is less than 12V or you turn your lights or other accessory on immediately after firing up, it may not "selfexcite."

With no resistors, it drew around 2 amps if I remember right. We don't want that much extra draw while trying to start the car as the spark is weak enough while the starter is cranking, and, with low voltage, it might not start the alternator any better than a small draw.

I experimented various resistors and finally settled on a group of small resistors in parallel that reads 115 ohms, but was likely shooting for nominal 120 ohms as my target was .1 amps. This only draws that tenth of an amp while the alternator is not putting out as the armature will feed the field once generating. Nice to know that isn't going through the ignition switch on top of all the other current. Even with this feed, the alternator might not kick in until it is revved up to bump up voltage. The higher the resistance, the more revving it would need to kick in if your batteries aren't already sitting at 12 1/2 volts.

That field wire needs to come off of a "switched circuit" through the ignition switch; if it were hot all the time, the battery would drain dead.


Sorry to disappoint you, but it isn't any better charging at idle than the generator. As it physically resembles the generator, I'm willing to bet it is not a 3 phase or multiphase device but only a 2 pole frame and does not APPEAR to generate 12V at idle. Why I say "APPEARS" is, with headlights and other accessories drawing noticeable current, the system voltage will drop to about 10V at idle and the ammeter goes negative, just like our old generator. It is still putting out, but not like conventional car alternators.

I installed a voltmeter years ago and it really helps to interpret what the heck is going on, or not going on.

I didn't put any effort into hooking up the charging light for the alternator since there's the voltmeter in the instrument cluster.

These thing are advertised for about 45 amps, but with the headlights, driving lights, emergency flasher, wipers, heater, backup lights on, and horn the ammeter says it is putting out maybe half the rated current, which is nice to know since I plan to add a couple of electric radiator fans. Might find that 45 amps if I install a radio with 5000 watt amplifier!

By the way, I cannot hook up a tach drive to the back of ours. The input shaft in the reductioin drive is too large to plug in... even bought a complete new batch of components from Abingdon Spares and they don't fit.

Did anyone get a tach drive to thread on?


Yes, it threaded on perfectly in my case.
Dave H

Dave Hill

Thanks for the info, Jim. About a year ago I had to give myself a crash course in alternators when a hammer mechanic screwed up the wiring of the charging system of my daughter's 1990 Dodge pickup. Learned about the need for that excitation voltage.
I've got that same concern about Mort's hookup. The old regulator functions could cause an intermittent oscillation in the field line.
So far Lazarus has tolerated 1 to 2 hour parade runs chugging along in first gear at about 500 rpm with the brake pedal down. It avoids running over the color guard in front of us. It's that left leaning ammeter needle that bugs me. Instead of the Dynamator I had Santa give me a pair of LED rear lights to lose the incandescent stop light bulb.
Here's Lazarus in the recent local Veterans Day parade pushing the flag bearer. Bud

Bud Krueger

Hi jim,

Yes I had an issue with the thread for the tacho gear box on my Dynamator. It stars fine but appears to bottom out before the gear box is secured. It maybe a problem with the gear box knurled nut or I may need to make a packing piece. At the moment everything works well so I am leaving the box loose until the weather is warmer and I will then investigate.

Jan T
J Targosz

Jim N...I had no problem with the tach.

Attached is a sketch of what I did. Mind you I switched from EE to CE in my first year of engineering school.

Jim, you wrote...

You did rewire it eliminating the old regulator, right?
((I did not gut the regulator. There is no power going to terminal A1. I just used terminal A as a junction point to run the ignition switch wire to the ammeter.))

Might be the DC regulator cutting in & out if it is still hooked up.
((Is this possible with no power to terminal A1?))

I stuck one in a year or so ago and it took quite a bit of headscratching to understand:
1: Why it didn't start charging after starting the engine;
((I am also having problems with charging my battery.))

2: How much resistance to add for the field lead since there were no instructions nor explanations;
((Which is the field lead(remember I'm a CE). Is it D or F? I have tons of resistors in the basement from an old project.))

3: Why it appears to stop charging at idle like the old generator.

((Will inserting some resistance in the circuit solve these problems?))

And once again thank you all for the help.


Mort Resnicoff

It is likely your regulator is the fly in the ointment.

I haven't messed with a Lucas regulator in decades. I revamped our TD wiring and used a pretty Edsel aftermarket regulator with a clear cover so you could see the internals; there were only 3 terminals. I'd have to reread the Lucas regulator functions to figure out which terminals are for what. The generator power had to be isolated from the rest of the battery fed components via the "cutout" points so the battery wouldn't drain when the generator wasn't charging; alternators solid state diodes made that set of points unnecessary. Hooking the alternator to that same post as the gen output would not seem logical, but I have to defer to the guys that have installed theirs with the Lucas regulator in place as to exactly why they gutted them and what terminals were used.

As for the alternator field, wire it through a resistor to any line that is powered off the ignition switch. The field terminal on the regulator is likely to be inappropriate for the task, but that shouldn't cause your ammeter to swing erratic, that's likely the current output hooked to the regulator.

More to follow.....

I googled "Accuspark MG alternator"

and discovered some interesting info:

I was wrong in that it is a 3 phase construction;

They show something that might be "5V" feed to the field;

What is most intriguing is the spec stating "zero-amp frequency" and show 1100 rpm "cold state" and 1150 rpm "thermal state." I'd have to interpret this to mean it ain't gonna putting out anything at idle!!!

There's also some separate installation tips for pos & neg ground cars

Note the warning that a relay must be used with the field circuit for positive ground!!!

Interesting they show a light bulb in what seems to be the field circuit and not a resistor. In either case, it'd be nice if they gave a hint as to the resistance. Maybe that blurring 5V was supposed to be the hint. My guess would be a small instrument light bulb as opposed to taillight bulb which could pass nearly an amp. Our TD generating light might work or just may be too low the way it has a resistance wire wrapped with it.

Do you have positive or negative ground?

I have to assume you have the correct unit for your ground, otherwise, your have described a welding arc when you tried to wire up the heavy lead, but that field circuit is a bit mysterious.

By the way, your "Accuspark circuit" in the bottom right of your image would only show discharge and never any charging. It would need to be located closer to the battery like where you show the cutoff switch, before the branch off to the ignition switch.

AND WITH THE RELAY FOR POSITIVE EARTH... without a resistor or light bulb, after the relay, the relay would close and then have no voltage and thus no power to stay closed, and just reopen... it would likely clatter open and closed. It still might work but not like it was designed. I wouldn't count on your regulator wiring to include the ign lamp correctly since the heavy lead goes there originally and not the field.

It's 3:30 AM, time to quit thinking about it.

Hi Mort. You still have your RF95 functioning in your configuration. The field circuit is tied to a set of relay contacts along with the dynamo field resistor. Terminal A1 doesn't 'receive' power, it's a 'source' through series windings of the regulator. I can see how the regulator is affecting your Dynamator's field circuit (BTW F is for Field, D is for Dynamo).
More later, family things are pressing. Bud
Bud Krueger

Tell me if this is correct.

Instead of using terminal A on the regulator as a junction point I will remove those two leads and just put a wire nut on them for now.
(I will move the horn lead from terminal A2 to terminal A4.)

On my third regulator sketch I show wires from terminal F and D but they go to nothing. There are no wires on those two terminals.

This should isolate the upper section of the regulator sketch from any electrical connection with the rest of the car.

Mort Resnicoff

Your diagram threw me off as you have ignition switch, ammeter and horn clustered together and then show a line to everything else. Your description revealed the horn isn't connected to the igniton switch/ammeter connection. Good, erase that line down to A4, and tie your horn wires to the ign switch/ammeter connection, that way the horn will honk without needing the ignition on. Your switch will appreciate not handling all that extra current. You also connect the alternator heavy lead here.

Power will run up to the ignition switch and then back to A3 where the front pump, heater and coil will be work unprotected and then tie to A4 where all that hardware has a fuse keeping an eye on things.

I would use an ohmmeter to first check that A3 and A4 terminals have zero continuity to ground.

As for the alternator field terminal, according to Accuspark, you can connect it to the yellow "ignition warning light" wire previously connected to D. That assumes that trickle from that small bulb with its resistor wire will stimulate the field adequately. If not, you can add a resistor in series with the field and tie it into A3 or A4 and then connect your yellow wire to the ign/ammeter/horn/alternator connection.

Unless you are adding a radio & 5000 watt amplifier to your car, you won't need to run heavier wires than stock.

Good luck!


Did you mean terminal F in this sentance?

"As for the alternator field terminal, according to Accuspark, you can connect it to the yellow "ignition warning light" wire previously connected to D. "

Mort Resnicoff

BTW Jim, years ago I added a 16 position fuse block and rewired the car so virtually everything on the car is protected with its own fuse.
Mort Resnicoff

No, "ignition warning light" thin wire, yellow and #25, hooked to "D" the generator heavy "Dynamo" terminal. The generator output was also yellow and #25 but must be heavier and should connect with the ign/ammeter/horn group.

The generator field wire is yellow with green and was regulated through field terminal "F" but it is defunct in this case.

As mentioned above, you may be successful hooking the yellow/green field wire to the ignition warning light yellow wire, period. You'll find out when you blip the throttle and see the ammeter jump to the charging side. Keep an eye on it as we'd take off and turn back from home since it wasn't charging. After a couple of those episodes, I showed my wife a hot wire I strung to touch to the field where we jump started the alternator. I juggled a lot of resistors until I was satisfied with enough field current (approx 0.1 A) for cold days, low battery voltage or lights turned on before the alternator kicked in.

If it doesn't generate current, you may look at finding a 100 ohm resistor and then hook field wire + resistor to A3 or A4. In this case, "ign warning light" should work when thin/yellow/25 wire is tied to the ign/ammeter/horn/alternator junction.

I used 20A circuit breakers for everything, even sometimes put a pair in parallel for makeshift 40A. Nice not to have to hunt for a blown fuse.

Keep your fingers crossed!

I mentioned "As mentioned above, you may be successful hooking the yellow/green field wire to the ignition warning light yellow wire, period." Your sketch illustrates the relay which conforms with the alternator providers crude schematics. Is it installed per your drawing?

Mort Resnicoff


Attached is a sketch of my current alternator circuit.

I have gutted the regulator.

I had a fully charged battery reading over 14 volts.
The car was extremely hard to start. It turned over many times but did not seem to get a spark. Eventually, it started but the ammeter on the dashboard bounced around on the negative side even at high RPM.

Should I open the connection from the field on the Dynamator to the ignition lamp and put those two leads on F and D on the regulator? There is still a large 63 ohm resistor between those two terminals.


Mort Resnicoff

I commented before, that the location of your ammeter only tells you what it is drawing from the battery and alternator combined. It is only swinging negative. It cannot tell you if it is charging the battery or not.

You need to put the ammeter between the battery and the junction to the alternator+car, then it can show whether the battery is charging or discharging.
Try tapping it between the battery cutoff switch and the vertical light line, that way you'll monitor what goes to and from the battery, discharge or recharge.

Straighten out the ammeter so you can really tell what's going on. It may already be working and you not know it.

You haven't confirmed it is positive ground but all discussions indicate that. Is it in fact positive ground?


Don't bother with your extra resistor right now, but you may just want it later to reduce the field draw at starting.

You have the light bulb in the circuit which is their idea of suitable resistor and should work. Who knows if they are aware of the extra resistor wire or what they had in mind for a bulb. IT would be helpful if they put that tidbit of info in their specs- field resistance / field current.

See what it is doing after restringing ammeter cables.

It would be nice to know what that resistance is, but you have it drawn according to their circuit. Maybe later check it with an ohmmeter for finer tuning?

Here's some good info on the subject of that "idiot light"

Yes my TD is positive ground.
Is this what you are suggesting?

Also, any thoughts on why it is so hard to start?


Mort Resnicoff

I believe this is what you are proposing.

Mort Resnicoff

Much better. Ammeter will indicate battery charge and discharge.

I just posted this on the wrong thread so i will repeat it here.


I just recently got a chance to work on the car.
This is a copy of the email I sent to the manufacturer.
Thoughts appreciated.

The attached schematic shows my current wiring.
It does not appear that the Dynamator is charging the battery.
I would very much appreciate your analysis.

I have the Dynamator installed.

When I activate the battery cutoff switch I get a negative reading on the ammeter of about 4.5 amps.
I get this reading with the clamp on ammeter between the ammeter and the cutoff switch and between the ammeter and the Dynamator.
I get no reading on the jumper from the ammeter to the ignition switch.

When I start the car the ammeter stays negative until I pass about 2500 RPM.
Below 2500 RPM it returns to a negative reading.

The system is not charging the battery.

Mort Resnicoff

Just for the heck of it, pull that field wire and see if that current disappears. If it does, then your relay isn't functioning right and your ignition lamp would glow when the battery cut off is switched on with ignition off. Your lamp really couldn't pass that much amperage, bit it is worth investigating to look at one more piece of your puzzle.

If that doesn't remove that draw, I'd suspect you got a defective alternator. There should be zero current back feeding into the alternator. I just went out and double checked ours and there isn't even a milliamp draw. The diodes act as check valves to ensure current runs only one way. The old regulators had to have the cutoff circuit to prevent the battery from draining through the generator. With that 4.5A leakage, you'd have to use your battery disconnect every time you park or you'll have a dead battery the next day.

The fact that it is charging is a good sign, anyway. The voltmeter is a better indicator of alternator behavior, but that parasitic draw has got to go before getting concerned with the rpms.

You could always ADD A BLOCKING DIODE external to the alternator to stop the loss, but that is just a bandaid on a bullet wound. They need to make good on the new alternator.

Out of curiousity, your circuit shows your field current goes through the ignition lamp as they recommend. When you turn the ignition on, it should light up. Is it lighting up?

When charging, the light should disappear. Does it?

I can't tell you if it'll brighten up on discharge, as we aren't knowledgeable on their voltage regulator/field circuit and our TD's field doesn't include the ignition lamp.


Just a sanity check but do I have these wired correctly?

"Just for the heck of it, pull that field wire and see if that current disappears. If it does, then your relay isn't functioning right and your ignition lamp would glow when the battery cut off is switched on with ignition off. Your lamp really couldnít pass that much amperage, bit it is worth investigating to look at one more piece of your puzzle."

Pulling the F wire has no effect.
Pulling the D wire with the battery switch closed reduces the drain to zero.
With the engine running the drain is about 6 amps. When I pull the D wire it drops to about 2.5 amps. That is the drain from the coil.

The ignition lamp does not light up at any time.

Mort Resnicoff


Your wiring is consistent with our "interpretation" of the Dynamator circuit. (copy & paste this to a new page if clicking doesn't bring it up)

If you look at their "drafting protocol" on the top sketch of positive ground "Control Box RB340 with Dynamo" (ie original wiring schematic with generator) you'll notice they loop the one wire over the other indicating they are not connected.

Now look just underneath at "Control Box RB340 with Dymator" there is no loop where the wires from power out and field cross. It is sketched goofy! Why does that field line run left, up, and then right crossing over the power lead?

If you interpret those wires DO NOT CONNECT, as I must assume, then your circuit is correct.

BUT, if they DO CONNECT, then we're wrong. Based on our alternator with negative ground, the field would have a significant drain (maybe 5 A? ...sound familiar?) as soon as your battery shutoff is closed, there is zero resistance to the field and the ignition can't shut it off!

We don't really have a clue how they wired the field and voltage regulator, so it is hard to interpolate which schematic is correct.

If you look at the negative ground schematics, they show the wires crossing over the same way, but I'm dang sure not going to live with a 5 amp draw 24/7.

I have a feeling you're dealing with one group that just markets them but the engineers of the Dynamator speak Chinese.

If you look at the Lucas Dynalite positive earth schematic, you have it sketched correctly.

That fact that the ignition light never lights up, the field terminal is not being energized through the bulb and relay.

When you're running tests, jot down what the voltmeter displays, too.

If I were you, I'd copy this post and send it to them.


After a month of troubleshooting and emailing back and forth to the supplier in England I finally have a resolution.
The alternator was faulty and they have sent me a replacement which is now installed and functioning properly.

I want to thank everyone who pitched in and helped with the problem.

I want to thank Jim Benjamin and Frank Filangeri for your emails.

And special thanks to Bud Krueger and Jim Northrup for your help troubleshooting the problem.

Mort Resnicoff


Glad you finally got it resolved and that Dynamator and the vendor stand behind the product. Happy to say both are working well in my cars.

F Filangeri

We've documented the work of Mort and Jim that resulted in Mort's success with the Dynamator in a positive ground car, complete with ammeter. It's in a few new web pages on Ttalk. See It's still under construction so I'd suggest renewing your browser whenever you open the pages. Bud
Bud Krueger

This thread was discussed between 26/11/2018 and 17/01/2019

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