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MG MGB Technical - Need Urgent Electrical Help

Just got home from work. Noticed my alt. light didn't turn on and my indicators weren't functioning. As a matter of fact everything looks like its low on power. Seems my alt. isn't putting out any juice. I changed the bulb but it still won't charge and the alt. light still won't go on. I grounded the light and it turned on so I know the bulb is working but the car still won't charge, alt light is off and my turning signals still won't work.

I found one of the plugs on the back of the alt. had come off, Ive since put it back on, but it still won't work.

If the plug was loose and caused a short (therefore burning out the alt) would this cause the alt. light not to come on?

Any wild guesses, I need the car for tomorrow at work.

Luis
'69 B w/ Bosch conversion.
Luis

I was in a hurry so I'll re-write and clarify the above a liitle.

When the key is in the start position, the alt light does not turn on. The bulb has been checked and does work so its not that. The car does not seem to be charging last time I tried, although I am now placing the battery on a trickle charger overnight.

One of the main large wires on the Bosch alt had become unplugged while in transit and I am afraid this may have wrecked the alt or something else by grounding out. I do not think it had been a long time that the plug had fallen out, perhaps five minutes no more. And as the Bosch conversion has two of these large wires from the starter it is almost redundant. Maybe I can get one of the MG gurus, Paul or Bob, out there to respond.

In no rush now as I've decided to take tomorrow off to trace down the problem.

Not too cheery,
Luigi
Luis

I almost forgot.

Another important symptom seems to be that the instruments went off and back on by themselves a few times.
Luis

Luis. Until someone truly competent can respond, I will share the little I know. I had a very similar situation, caused by time, not checking properly and stupidity. Got the engine back in late at night, hooked up everything but the alternator plug and ran in the new engine. Alternator did not work after that and had to be replaced. I think I would pull the alternator and take it in for testing if it were me. Les
Les Bengtson

I will second Les' recommendation. Take the alternator in and have it checked. Having been run in an open circuit condition could have fried the diodes. Good luck - Dave
David DuBois

If by testing the warning light you mean you grounded the brown/yellow in the alt plug (plug removed) with the ignition on and it lit, but doesn't light when plugged in to the alt, then the alt is definitely bad. I ran an alt for about 30 miles with the plug out and had no lasting damage, but having the brown off but the brown/yellow connected could be different.

Turn signals glowing but not flashing *is* a symptom of low power, like when the alt is not charging. If the instruments went on and off a few times, this could be caused by the thick brown from the alt having touched the block or some other grounded metal work and drawing a large current. However *because* the instruments went off that indicates there is a poor connection somewhere, probably at the solenoid stud, which will have prevented too much damage to the wiring. So when you get the alt fixed, clean up the solenoid connections as well - battery disconnected (ground strap first) of course.
Paul Hunt

Well I charged the battery and tried this morning. The instruments still didn't go on and after a minute or two of ignition on Inoticed the coil was way too hot to touch. Don't know if that went bad or not so I changed over to an older coil to make sure and all the instruments came back on line. Started the car but the alt still didn't charge. The alt light still didn't turn on either. Have now taken the alt to the shop and they've checked it out. Looks like I did some damage somewhere inside and it'll need rebuilding. Min $75, damn.

Is it normal for the coil to get so hot in so little time? And did the instruments suddenly come back after changing out the coil? Could the coil have become damaged because of the short?

Waiting for the Bill,

Luis
Luis

Luis,

I have an extra lucas alternator (i switched to delco)...if you want it, it's yours for the shipping cost...just post your email

rn
RN Lipow

Coils can get very hot if the ignition is left on without the engine running - about twice as hot as when running. The loose alt wire is unlikely to have damaged it. The instruments should work off the battery, so if they didn't but the coil did then you have other problems, like at the fusebox.
Paul Hunt

'lo all

As far as I can work out, there should be no reason for a spinning, disconnected alternator to toast itself. Even if there were enough residual magnetic field present without the field coils being powered through the bulb, it would just create voltage as normal. The regulators would notice that there was no current draw and limit the voltage on the field coils so that the voltage didn't go high enough to break down any semiconductors.

The main problem though is that having one B+ wire flying around under your engine bay could have done all sorts of damage. If it was arcing against something then the current/voltage transients could have caused a dry joint to give up totally (check all your fuses for corrosion) and the extra current drain of a short could have damaged the alt (although it's supposed to limit its own current output).

Before you replace the alt, double and triple check all of your wiring with a good meter, engine running, so you can see where any voltage gets to.

Good luck!
--
Olly
Oliver Stephenson

Thanks to all.

RN: Thanks for the offer, but I've decided to stick w/ the Bosch.

The regulator was shot on the alt, probably because of the loose wire coming into contact with the case. Another problem was with the Alt's rear bearing (case?), it was shot (this from a "rebuilt unit" at Discount Auto Parts. Now I know why the parts are discounted). The coil? I dunno, but I did replace it and the instruments are Okeedokey now.

I also got a new plug (the right one) for the back of the alt. Its hell to take off once its on so I think It'll do.

I'll go over all my wiring and check all connections as advised, so I'm hoping this will be the end of my trauma.

Thanks to all.

Luigi
Luigi

This is why i went Delco on my B. I replaced three bosch "rebuilts" before returning the last one and demanding (and getting) my money back. The Delco has been reliable (so far) and powerful.

rn
RN Lipow

Probably the simplest alternative alternator to wire in where it was never designed to go is the single wire Delco. As long as the rebuilder does a good job with good parts, and is willing to back it up with a good warranty, it is as good as any other alternator at doing its job. And, the same can be said for any Lucas, Bosch, Hitachi, Mopar, or Nippon Denso alternator one buys rebuilt.

I have had very good luck with the Bosch unit I installed some years ago on my B, no problems with it or the wiring, and the car it went into was never set up for an internally regulated alternator, a bit more to contend with wiring-wise than most of the conversions people have sent me comments on.

As I have said here before, I can only vouch for the performance of Bosch rebuilts refurbished by AUTOLITE with a LIFETIME warranty ~ they seem to be more consistently good than what some folks have installed from apparently other rebuilders. They are not cheap rebuilts, but on the other hand, I have not had to replace the two I installed on two different cars, warranteed or not - they just keep on chargin'. As with any rebuilt anything, rebuilders are not all created equal.
Bob Muenchausen

Is this a true 'single-wire' alt, i.e. no ignition warning light terminal? Elsewhere recently there has been discussion on this and claims that true single-wires are very expensive, as well as confusion as to what 'single-wire' actually means. They also need a voltmeter (or an ammeter) to be installed as the warning light function is lost. And if the indicator wire is already there I must confess I can't see how a single-wire alt is a simple alternative.
Paul Hunt

Bob and Paul,

As far as I know, Delco never made a "one-wire" alternator. The standard "SI" alternator can be converted to a one-wire by the installation of a special control module. This module can be installed by a commercial supplier or can be purchased and installed by the home hobbiest. Both Summit and JEGS sell this module. The addition of this extra module makes the cost of a true one-wire higher than the standard Delco SI three-wire alternator.

Unfortunately, way, way too many people, including most auto parts store countermen, believe that ALL Delco SI alternator are onw-wire. As I mentioned on the other thread on this same subject, one of the most common calls for help that I get on alternators is from someone who has installed what they were told was a one-wire, connecting only one wire as instructed, and then finding that it doesn't work.

A three wire SI will run around $25 - $30 here in the US (I paid $26 for the last one I bought a couple of years ago), whereas a true one-wire will run close to $100 (usually chromed as well).

I have written a complete set of instructions for converting most models of Triumphs to a GM/Delco alternator at http://www.vtr.org/maintain/alternator/conversions.html Even though written for Triumphs, they will also work for various MGBs as well. Just find one that matches your MGB and have a go.

Check out MAD Enterprises http://www.madelectrical.com/ for more info on this. Mark Hamilton, owner of MAD, has written a good article on the pro-and cons of using a one-wire vs a three-wire.

It is my understanding that the Bosch alternator is a much easier installation in an MGB than the Delco, but is more costly and less readily available. An alternator is an alternator is an alternator, so any model (12 volt) that will fit will work - just that some are easier/cheaper than others. If you happen to have a good one laying around from, say, a Suburu, Honda, Toyota, Buick, Cadillac, etc, and you can make it fit, go for it.
Dan Masters

What I was referring to Dan, was that most people I have encountered who want to install the Delco alternator (SI) are really referring to the single wire unit they see in the catalogs, not usually the three wire unit as GM designed it. They are looking for hookup simplicity, and believe that this is the way to go.

You are quite right that all makes do the same job, regardless, and frankly, the longest lived in my experience (and perhaps then, the cheapest per mile????) are many of the japanese units, such as Hitachi. I thank you for sharing your insights on this via your Delco site and MAD's, something that my Bosch site has no intention of covering. I will add both yours and MAD's sites to my links there in the future. It doesn't matter to me which unit anyone chooses, I just tried to put one out to guide folks interested in doing the Bosch as it seemed a simple alternative for the MGB.

I would also mention that I think it doesn't hurt us MG folks to look over the fence at the sites our other british bretheren have put up, since we share so many components and construction methods in common. FWIW, a couple of very good sites in general are: http://www.buckeyetriumphs.org/index_technical.htm and http://clubs.hemmings.com/clubsites/capecodbritish/technical.html



Bob Muenchausen

This thread was discussed between 24/10/2002 and 04/11/2002

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