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MG MGA - The Prince Strikes Again


Application: 56 MGA with 1800 engine, original type generator, voltage regulator and Petronix ignition system.

As I started my car this evening when departing our local MG club event, the generator light was on... and it stayed on. The headlights were not as bright as they should be. Obviously I was running on the battery. My battery is less than a year old, so I thought I could make it on the battery the approximately 10 miles from the event to my garage. I did, but barely. The last mile was driven with with the lights turned off and the car backfiring.

So now I need to figure out if it is the generator or voltage regulator. I checked the archive and found the thread on how to check the generator and regulator after changing the car's polarity. It states:

"Double-check the generator/dynamo - once correctly polarised - by disconnecting the wires from its terminals, connecting the two terminals together and to a 20v voltmeter. Start the engine - DON'T rev it!! - just slowly increase the revs watching the voltmeter. It should get to 20v by the time you get to 1000 rpm. DON'T exceed 20v. If that checks out reconnect the wires to the dynamo with the voltmeter on the D terminal (brown/yellow wire) and again start up and slowly increase the revs watching the voltmeter. The voltage should rise then stabilise at about 14.5v, it it goes higher again don't let it go over 20v. If it stabilises at 14.5v it is charging OK but I guess it won't be. If the D terminal shows only about 1v there is a disconnection in either the brown/yellow or the brown/green between dynamo and control box, or a fault inside the control box."

Can anyone offer any other advice on how to check whether my problem is in the generator or voltage regulator? If it is the generator, I'm thinking it is time to convert to a Moss alternator kit. Has anyone had any bad experiences with that kit?
Frank Nocera

1) Charge the battery up.
2) Start car and set idle to 1500 RPM
3) Use VOM meter and check the voltage between the D terminal of the regulator and ground. Voltage should be around 14.5 volts.
4) If the voltage is over 12.6 volts but not up to the 14.5 volts with a freshly charged new battery then most likely the regulator needs cleaning and adjusting.

5) Get a copy of the Lucas trouble shooting manual. Someone's always selling reprints

Blake
Bullwinkle

Frank
Do yourself a favour and make the switch. I wasted 2 months of screwing around trying to figure out what was up with my gen. and or volt. reg. I finally gave myself a good shake and bought a Lucas alt. for a 1977 MGB from a local parts dealer and the rear mounting bracket from Moss and relocated my coil to the inner fender. I followed Barney Gaylord's instructions on using the existing volt. reg. as a terminal block and was up and running in 30 min.
Kris
Kris Sorensen

Frank - Kris' suggestion makes a lot of sense and will correct a multitude of ills, such as the lights dimming every time you stop at a signal, etc. That said, if you are determined to stay with the generator, then do the check on the generator. If it fails, the problem is the generator, if it passes, the problem is either the wires between the regulator and the generator or the regulator. If you are doing this check, you should use a analog multimeter, not a digital - it is too easy to get goofy readings on a digital. set the multimeter for 25 or 50 volts depending on the scales on your multimeter, and hook the negative lead (if you have a positive ground car) and the positive lead to ground to do this test (reverse the lead connections if your car is negative ground). If the test passes, switch the multimeter to read ohms and check from end to end of each of the wires going from the regulator to the generator for 0 ohms (be sure to calibrate the meter by shorting the two leads together and adjusting for 0 ohms first). Set the multimeter to read the highest ohms and, with both ends of each wire disconnected, check from either end of each wire to ground - this reading should be infinite. If the generator test and the check of the wires are both sat, then the problem is in the regulator and you will need to follow the procedure to adjust it. Don't worry about repolarizing the generator, if it was working previously, it is polarized correctly and a generator doesn't just up and decide to change it's polarity overnight. Now that I have led you labouriously through this troubleshooting procedure, I shure hope that you aren't a EE or have worked in electronics for the past 40 years or I am going to feel like a jerk :0 Cheers - Dave
David DuBois

Hi, Frank - you may be looking for a good argument to change to an alternator, and all of the arguments are good unless you absolutely want to stay original. If so, you can download the Lucas manual entitled "LUCAS Generator and Control Box TESTS", and dated 1963, at this site:

http://www.1978mgmidget.com/manuals_and_booklets.html

There's a couple of MGA manuals on the site, too. Cheers - - alec
Alec Darnall

Thanks, guys. Luckily I have an old analog VTVM and this morning it confirmed a fried generator. I have ordered the Moss alternator kit. I know there are probably many out there who will attest that a good rebuilt generator and new voltage regulator are just as reliable as an alternator. I am not one of them. I have done a lot of "bolt-on" mods to my '56 A (front disc brakes, Petronix ignition, Sierra 5 speed tranny, 3.9 rear end, modern fuel pump and trailer hitch), so as you can see, I am not a stickler for originality. I want my car to be one in which I can take weekend road trips with confidence. Time to add an alternator to the list of completed mods.
Frank Nocera

This thread was discussed on 16/01/2005

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This thread is from the archive. The Live MG MGA BBS is active now.