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MG Midget and Sprite Technical - More 76 wiring questions

More wiring "issues" with my 76 midget 1500. I have 3 wires (in the vicinity of the coil) that have continuity when checked with the white wire coming off the ignition switch. There is a double white with green tracer wire, single white wire, and a single white with green tracer wire. Which goes to the coil and where do the other 2 go? I have the D25 distributor, not the electronic one. Do any of there go to the oil line sensor? See picture. The Haynes manual is helpful, but does not tell you all. That is why we depend on Y'all!! Thanks ....AL


AL MILLER

Hello Al

OK your wiring appears not to be standard so what have you.

Normally with a ballasted coil system you have 2 White with Light green tracer wires.
One of these sould be a low voltage wire, (about 8 volts permanantly when ignition is on) the other comes from the starter solenoid and will have 12 volts on it when the starter is engaged (starting) This will go open circuit when the starter has been released. Then these 2 will go to the positive connection of the coil, on the other side of the coil should be a white wire with a black tracer that connects to the wire at the distributor. Therefore what is your wiring?

You need to check these 2 white and green wires and also find the white and balck tracer that fits to the dissy?
Robert (Bob) Midget Turbo

Not sure if this will help...mine's a '78 and appears to still be virgin at the fuse box...looks like you have a bit of creative wiring there (necessity is the mother of invention!)

If I can figure out this upload stuff, I'll send a pic.

Dave


DL Rhine

Oops...put on the wrong wiring question thread!

Good luck...

Dave
DL Rhine

Al,
I imagine that what you are seeing is the left-overs from converting from the electronic distributor to the earlier (more reliable) points distributor. All you really need is for there to be a white wire to the + of the coil and a wire (originally white with a black tracer stripe) from the distributor to the - of the coil.

One of the white/light green wires came from the solenoid to bypass the ballast and provide a full 12VDC to the coil while the starter is engaged to enhance the spark. Another one came from the ballast resistor. The white was probably there to power the electronics of the dissy.

Now, the real question is what to do from here. You are really better off without the troublesome Lucas electronics, especially since they are already gone. You need to find out whether your coil is internally ballasted, so disconnect everything from one side of the coil and measure the resistance from the + to the - of the primary. You should see either 1.5 ohms or 3 ohms. The original coil should have been 1.5 ohms, but the 3 ohm coil is correct for the points distributor. I would recommend that, unless you want concours-correct, you make sure that you have a 3-ohm coil and run a white wire to the + side of it (with the key on, you should see 12VDC from the white to ground) and run another wire from the points connection on the side of the distributor to the - side of the coil. If your tachometer does not work come back and let us know, but it should be fine.
David "dizzy yet?" Lieb
David Lieb

Dave, thanks again. I have to get to bed so I can figure this all out .....AL
AL MILLER

Been there... for what it's worth, that solid white wire with the "elbow" connector on the end originally connected to a resistor mounted near the coil; there was another wire that then ran from the other end of the resistor to the distributor. The white wire, as you noticed, supplies a switched 12V.

Now don't confuse that distributor resistor with the "Ballast resistor" that some cars have in the power wire to the coil. This was something different. The 1500s DO use a resistance upstream of the coil, but this is managed by a resistance wire in the harness. Robert (Bob) explained the function of that gimmickry very well.

So if you have a non-original distributor, that white wire will be unused.

-:G:-
Gryf Ketcherside

Dave,

I checked and my coil has a 1.5 ohm resistance to it. I also have an (aluminum) ballast resister that looks like was mounted on the coil hold-down strap. It is an original Lucas and has a resistance of 9.3 ohms. Thanks for the Lucas wiring info. It will come in handy. Because I have the original coil, I guess I have to put the double WG wires on the + side and the single WG wire to the starter solenoid, and then go from the - coil side through the resistor to the distributor. Right?? My wiring all appears to be original in the area of the coil and the distributor. Again, thanks for your awesome knowledge. Email me direct if you prefer ....AL
AL MILLER

AL:

In your picture, the wire at the back of the paired wires appears to be white/blue, not white/green. If so, then that MAY be the resisted wire (from the externally mounted resistor near the coil) that originally went to the stock distributor. Why it would be paired with a white/green wire is a mystery. If it is indeed white/green like it's companion as you say, then it is as probably as Bob says above, the pair of wires that would have run to the positive side of the coil.

In your other current thread you mis-identified a slate colored wire as brown. Is it possible you mis-identified the color of this wire as well? There should not be three white/green wires in that area. The only candidate for a third white/green wire in that vicinity would have been the un-resisted 12 volt feed from the solenoid to the coil.

So: IF the wire at the back of the paired wires in your picture is indeed white/green, then a continuity test will (probably) show the single white/green wire in your picture(that used to attach to the solenoid) to be the other end of one of the paired white/green wires. If it proves to be white/blue, then you have a DPO (Dreaded Previous Owner) situation.

R
Richard 1500 5 speed

Not quite Al,
The aluminum ballast resistor is for the original OPUS electronic ignition. It has a solid white wire on one side and white with blue trace on the other. The white/blue ends at the three prong MOLEX connector that you'll find tucked in there near the coil. That connector had white, white/blue and white/black wires that went to the OPUS distributor.

You don't need it for points distributor. Just a wire from distributor to (-) side of coil. The negative side should also have a white/black to feed the tach.

The OPUS was notoriously unreliable and was replaced under warranty with a CEI ignition that works flawlessly, which is what I have in my car. Even better than Petronix IMHO.
Lee
Lee Fox

OK, to clarify I have the following wires in the coil/dist area: white, white with blue, double white with black wires, double white with green wires, and a single white with green wire. And yes, I do have the MOLEX connector (which adds 3 more wires to the equation!)There is also an oil sending unit in the vicinity which I suspect takes one of the wires. There are no slate colored wires, just a wire with primer on it!

To the starter relay I hooked up the large brown alternator wire, 2 large brown wires together, and 2 smaller brown wires that were together. Then, I put the white with red wire on the individual spade on the opposite side of the solenoid. I have the D25 Distributor with points. It all looks original to me, but because I am using an earlier model distributor I understand that I may not need all the wiring, but I am not sure on how to wire the coil and distributor. Thanks .....AL
AL MILLER

Al,
I'm emailing you a color wiring diagram. This will solve the puzzle.

Double white/green to (+) plus of coil
Double white/black to (-) negative of coil
Single white/green to starter solenoid
White to aluminum resistor
White/blue to aluminum resistor

Run your own wire from distributor to (-) negative of coil. Ignore the MOLEX connector.
Oil sender is white/brown, but should come off the wiring harness near the alternator.

Hope that helps.
Lee


Lee Fox

Lee,
If Al has a 1.5 Ohm coil, he will need an external ballast resistor when running with a points distributor or any other distributor. Not 9.3 ohms, however ;-) Personally, I would set this coil aside for the future possibility of desiring original crap and acquire a 3 ohm coil like the pertronix Flamethrower. At that point, you simply need a white wire to the + terminal and a wire fro the dissy to the - terminal and the brother of your mother is Robert.
David "my mother's brother is Bruce" Lieb
David Lieb

Al + David-
No.
The ballast resistor is built into the harness on all (OE) electronically equipped MG.

A (or several) White supply wire is spliced to a resistance wire in the harness. This is more or less below the fusebox, and the splice is visible since it is outside the wrapping. The resistance wire is a (the only)**glass braided** wire of varying color,white, red, brown,etc (must have been using surplus stuff). This runs out to the LH headlamp connectors (end of harness), and returns to whence it came. At that point it becomes the WLG, which supplies ballasted power to the coil+. The WLG is double where it connects to the coil, the second WLG being the 12V supply from the solenoid for hot spark on start.
So, the coil + has only the double WLG.

The coil - has the double WB wire only. One of these is the signal to the tach, the other one goes to the distributor. It's one of the three Molex wires, cut the plug off.

You will have ONLY a double WLG on the coil +, and ONLY a double WB on the coil -, and only a single WB on the dist.

For neatness and less confusion in the future, cut the harness wrap enough to get rid of the WU wires, and the aluminum "run resistor". I collect those resistors, very nice piece for other uses!

All this will leave you with one spare W wire, which is valuable for anything you want key controlled, or to use a 12V non ballasted coil, or a coil with a separate ballast. It's hot w/ key ON, so tape up the end. Rewrap the harness with the spare W sticking out but taped down so you know it's not "active" but it's still available.

FRM
FR Millmore

Slight correction: You may have two spare W wires left, depends on some variations in wiring for different years/models. Keep both available but isolated, never hurts to have them!

FRM
FR Millmore

Thank you FRM!

I found the location of the junction point of the three white wires and the (apparent) resistor wire that is shown on the wiring diagrams for the North American 1500, all model years (see pic). It is indeed outside the loom, as you say, near the clutch reservoir on my 1979 California spec car.

However, there is a pink/white wire you can see in the pic that is NOT shown on the wiring diagrams for my or any other 1500 car. It presumably runs to the resistive wire within the loom. I cannot find any visible sign of the PW wire in the location you say or anywhere else. I am tempted to open the loom cover to see if I can find the **glass braided** resistive wire itself.

As a point of curiosity and info for the archive can any other NA 1500 owners verify the location and color of this fourth wire?

R


Richard 1500 5 speed

Richard-
The KW (or is is WK? - first colour is main, second is tracer - important!)(pink = K, P = Purple) wire is the resistance wire, replacing the glass braided one; evidently they decided that the glass braid was overkill. Both the construction and colour of the resistance wire seems to vary randomly, with the braided type earlier. I believe that if you strip it you will find it to be a nickle alloy, not copper. This is a late change, after '77 and Midget only (not MGB)I think, inherited from TR6 and other Triumph. They also have some other differences, like a WY instead of the WLG. I've not seen it on MG, since all the MG - Midget & MGB - I've worked on are earlier.

Do all your other wires match the colours I gave? Your car would have come with the later electronic system, not the wretched early one; that may be the difference. Since the later system actually works well, I've not had to rework any. I don't have the diagrams for all these late cars; they may be available at Advanced Wiring or somesuch. This stuff is all out of my head, not out of my mind, we hope!

FRM
FR Millmore

Richard,

The white/pink wire is supposed to provide switched +12V to the radio inline fuse in the center console. It does not run through the resistive wire.

Only a single white/green goes through the resistive wire to the (+) positive of the coil.

FRM- What do you use those 'run resistors' for??

Lee "resisting the urge to make an electrical pun" Fox
'79 1500 FED-my resistive wire is white.
Lee Fox

Lee-
"The white/pink wire is supposed to provide switched +12V to the radio inline fuse in the center console. It does not run through the resistive wire."
>>>That's why I'm being picky about the colour nomenclature - it matters! Do you have a WK or a KW at this splice?

"Only a single white/green goes through the resistive wire to the (+) positive of the coil."
>>>Yes, but the second one, attached to a single terminal on Al's car, is the 12v bypass supply from the solenoid.

"FRM- What do you use those 'run resistors' for??"
>>>Turns out they make a splendid dynamic braking resistor for a 1/4hp variable speed DC drive, an option the mfr wanted like $100 or more for. Since then I've found other random uses; they're very nice and suit pretty high power applications.

"Lee "resisting the urge to make an electrical pun" Fox
'79 1500 FED-my resistive wire is white."
>>>Well, why not as long as it is current?
Seriously, is your resistance braided and visible at the splice?

FRM
FR Millmore


>>>That's why I'm being picky about the colour nomenclature - it matters! Do you have a WK or a KW at this splice?

---On closer look at Richard's picture it is pink/white and should go to the distributor. White/pink can supply the radio, but it is absent on my car.
See http://www.mgexperience.net/article/lucas-colours.html
At the splice, I have three white and the braided resistive wire, also white.

>>>Yes, but the second one, attached to a single terminal on Al's car, is the 12v bypass supply from the solenoid.

---same as mine.


>>>Turns out they make a splendid dynamic braking resistor for a 1/4hp variable speed DC drive, an option the mfr wanted like $100 or more for. Since then I've found other random uses; they're very nice and suit pretty high power applications.

---Cool!


>>>Seriously, is your resistance braided and visible at the splice?

---yes
Lee Fox

Main Color first, tracer second.

The K/W wire in question (see image posted above, and different image below) is DEFINITELY K/W, not W/K.

As it is in fact spliced to the 3 white wires I believe it to be the ignition wire junction shown on my wiring diagram. What other possibility is there really? I have not opened the cover to check if the K/W wire is copper or nickel alloy.

My radio keyed hot feed is W/G.

The coil positive wires we are discussing in this thread are actually W/LG, as Bob and David mentioned above, not green as we have been lately calling them. As long as we are trying to be accurate.

My car's wires match the descriptions given above by FRM and Lee.

Anyone else with a 1500 have this grouping of three whites and a 4th wire at this location, and what is the color of the fourth wire?

R




Richard 1500 5 speed

Lee-
I agree that Richard's pic shows KW, but since there is no braided wire at that point, and the KW is spliced to the 3xW, that must be the resistance wire.
The referenced article is excellent for later (post 80, or after all MGs we know) cars but not a lot of use on early ones. I prefer to stay with cars that don't need so many wires! The terminology "ballast terminal" is ambiguous - which end or both? It could come out at the dist/coil as either KW or WLG, makes no difference; the transition if any would be along the harness. It is said there are no splices inside the wrapping, so any change point should be visible, likely at the harness end by the headlamp, or somewhere closer to the dist. The delete of the braided wire implies lower temps, which in turn means more length to dissipate heat over a bigger area. Perhaps Richard will tell us what colour his dist wires are, though they would be CEI compliant. Should be the same as yours, one would imagine, but since your splice point differs, who knows?.

FRM
FR Millmore

<< On closer look at Richard's picture it is pink/white and should go to the distributor. >>

Yes indeed I believe so as well, but when it reappears out of the loom wrap it is W/LG, not K/W.

<< Seriously, is your resistance braided and visible at the splice?---yes >>

British Leyland was really flying cheap at the end, weren't they?

FWIW, I just checked coil positive voltage at idle: 10.5 V. Do different configurations of resistance wiring give different voltages at coil positive?

R
Richard 1500 5 speed

<< It is said there are no splices inside the wrapping, so any change point should be visible >>

A cursory look-see down the loom near the headlights where the wires are exposed shows no visible K/W wire. Closer inspection will be required.

I am obeying the voice in my head that's repeating: "do not take the cover off the loom", though I am sorely temped.

The CEI unit (no longer on the car) has a W and a W/B wire to the CEI from the coil and one R, plus one B wire to it's distributor.

R

Richard 1500 5 speed

I decided to sacrifice (portions of) the loom wrap on my boneyard 1979 Cal spec car. The K/W and the W/LG wires do indeed run forward in the loom with the headlamp and other wires, exiting, connecting, and returning at the front of the car. At least on 1979 Cal spec cars.

See image.

More light shed upon Lucas, Prince of Darkness.

R


Richard 1500 5 speed

Richard,
That's what I expected, same as MGB, except for the odd KW instead of the random coloured braid.
The WLG had to connect to the coil on the OE system, as I expect it does now.

"FWIW, I just checked coil positive voltage at idle: 10.5 V. Do different configurations of resistance wiring give different voltages at coil positive?"

>>> Maybe, and that is implicit in the different coil specs, but you are getting an average. The coil pulls enough current through the resistance to drop the voltage to 6 or 7 V under load, but when the "points" (electrogizmos) are open, no current is flowing, so there's no drop, so the voltage is at system level, around 14V. The meter averages it. OE coils are stamped with design voltage on the bottom, 6 or 7V for ballasted systems, 12V for non ballasted.

FRM
FR Millmore

Well, what do you know! My resistance wire pops out in front behind the grill, too and turns into a white/green wire that goes back to the coil and then to the solenoid.

Mine's white braid and Richard's is pink/white.

I didn't test to find out what the resistance really is.

Anyone know?


Lee Fox

Lee-
Been tryin' to tell you that!

The resistance should be about 1.5 ohm, since that is roughly the difference between the ballasted coil = 1.5 ohm, and the non ballasted ones = 3.0 ohm. The non ballasted ones have the resistance built into the coil. The advantage to the ballasted system being that you can bypass the ballast on Start (hence the WLG to the solenoid), to get a fat spark (briefly feeding nominal 12V into a nominal 6 or 7V coil) whilst the Batt V is down due to the starter draw, cold weather, etc.

FRM
FR Millmore

Yes, of course. Thanks.

My brain must have been in "Lucas" mode: one of three positions - Off, Dim or Flicker!


Lee Fox

This thread was discussed between 21/09/2009 and 24/09/2009

MG Midget and Sprite Technical index

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