MGB Multiple charging system issues: 67 MGB

[Tim_Cressman]

Greetings,

I’ve been lucky to find a 67 MGB, great shape little use over the past 15 years. I’ve probably drove it more the last month than the past 15-years. No issues at all for the 1st two-weeks when what I assume happened was my ignition system stayed live after I turned the ignition off (voltage regulator contact stuck closed?) and I suffered a major melt down.

1) generator severely fried
2) voltage regulator fried
3) wiring melt down of:
a. generator to regulator
b. regulator to starter solenoid
c. collateral damage of various wiring in harness

I replaced all the main components noted above and the damaged wiring. Performed exploratory surgery on the wiring harness within the damaged area and my conclusion was I’ve detected and replace all.

Go live after these repairs gave me two new problems:
1) 1st intermittent headlights and then no head lights
2) Ignition light remained on after the engine was running.

The head lights issue was really solve by replacing one light, but prior to that I
1) Replaced the head light switch with no success of repairing the light issue.
2) Inspected the head light wiring very closely for shorts.

The ignition light remaining on was solved when I finally managed to focus my 44-year old eyes closely enough on the wiring schematic to see that I had two wires at the voltage regulator reversed. These were the brown and yellow generator to voltage regulator wire and the brown and yellow ignition light to voltage regulator wire.

Swapped these to there correct post and thought I was laughing. Ran the car for a good afternoon trip, fired her up later that evening to find that the voltage regulator contact was sticking. Recognized this because the ignition light would stay on with the ignition off, and would not go on with the ignition turn to the on position prior to firing her up. Fire it up and the ignition light would go and stay on. By the way the afternoon trip I deduced later was not as good as I lead myself to believe because I was letting the joy of finally driving her lead me to ignore what I no believe was my generator frying itself. This happen during highway speeds at approx 70 MPH (and yes it has the large pulley on the generator not the small one).

Change the voltage regulator the next day with no results. That was when I disconnected both wires at the generator, fired her up and measured zero voltage from the generator.

Put another generator in it tonight, measured good voltage, ignition light off when running and took it for another ride. Just fired the second generator, once again only after some length of driving in the city, it fried at highway speed.

So; what the heck is going on.

Many thanks,

Tim [/font]

 

[zahnej]

Tim,

Welcome to the forum!!

I am not familiar with B's at all so can't help - sounds pretty weird. Keep watching the forum - there are some way smart guys on here and I'm sure someone will help you out.

 

[Sarastro]

Pretty strange, I'll admit. I can only guess at a couple things to look at.

First, are you sure the generator is dead? Is it physically burned, or just not working? You said there was no output without the wires connected to it, but you won't get much unless the field coil is energized. The standard test is to connect the field and generator terminals together, check it with a voltmeter at idle. Don't speed up the engine too much, because you can get quite a high output voltage.

Which brings up the second possibility. The regulator works by switching a resistor in series with the generator's field coil, when the output voltage gets too high. This reduces the generator output by reducing the field current. One of the relays in the regulator does this by clicking its switch contacts open at about 13.5V. If this doesn't happen, it could cause what you're seeing. There are straightforward tests for this, which are outlined in any shop manual. You do need to use a moving-coil voltmeter, not a digital one, because the electrical noise in the charging circuit will drive the digital meter nuts.

There is a current regulator relay too, which switches in the field resistor when the current gets too high.

A final relay in the regulator disconnects the charging system when the generator output is too low, so the battery does not drain through the generator and make it think it's a motor. If this didn't happen, it could conceivably damage the generator.

I think I'd start by making sure I had a working generator, then do the regulator tests outlined in the shop manual. I kinda suspect the cutout relay might be sticking--this relay is a kind of a latch, and once its closed, it tends to stay closed. A common error is to push it closed accidentally when working on the regulator; then it stays shut and can be hard to open; turning off the ignition may not open it. Meanwhile, you have a heavy current drain from the battery straight into the generator armature.

I realize I'm rambling a bit, but maybe some of this might give you some ideas.

 

[David_DuBois]

Tim - Sounds like you still have some wiring issues that need to be sorted out before you drive the car (or even replace the generator. When you say that the generator is fried, what are you basing this on? You state that you disconnected both wires from the generator and ran the engine and got no voltage from the generator - this is normal, with no voltage being fed back through the regulator to the field winding of the generator, you will not get any output from the generator.

Before you do anyhing else, go to: https://www.advanceautowire.com/ Click on Stock Schematics and copy the drawing for your car (better yet, download the whole file to a flash drive, take it to Kinkos and have them print it full size (I think that it is 14 X 17)and then laminate it. Now you can go through the whole charging circuit and determine if there is still a problem anywhere in it. I would suggest disconnecting the wires at both ends so you don't measure any sneak paths tha tcan eithe make you believe that you have continuity where none exists or that you have a short where none exists. After doing this, disconnect the two wires from the genrator and tape them off so they don' short against something. Use a short piece of jumper wire, connect the two terminals together. Set your multimeter (this has to e an analog meter - a digital won't give you the readings you need to watch and can result in damage to the generator) to the 25 or 50 volt range. Hook the red lead to ground (assuming that your car is still positive ground - if it has been converted to negative ground, then hook the black wire to ground). Hook the black wire (for positive ground) to the jumpered terminals of the generator (or the red wire if the car is negative ground). Start the engine, but don't rev it up. Watch the meter and slowly bring the engine speed up until the voltage reads 20 volts - don't let the voltage go above 20 volts as it will increase very rapidly beyond that point and can get high enough to damage the generator. If yo can get 20 volts out of the generator, it is good. If the voltage will not reach 20 volts the generator is bad, even if you can get 12 volts but not any more out of it.

If the generator tests good and you have gotten all the wiring sorted out, then I would suspect the regulator (they often come bad out of the box). At this point I would suggest that you contact Bob Jeffers at: bobj20@comcast.net, tell him what all you have done and what the results are and see what he thinks or suggests. Bob is the expert on charging circuits in general and regulators in specific. You can even send him your regulator and he will convert it to solid state and calibrate it for your generator.

One more thing, and I'm sure that Bob will ask the same qustion, have you polarized your generator to match the polarity of your car? If not, that needs to be done. e-mail me directly and I'll give you directions for doing that.
Cheers,

 

[Tim_Cressman]

Gentlemen,

Thanks for the detailed replies, great stuff that I will spend the day under the hood sorting through it.

The original failure was in fact a meltdown, no question to that; the subsequent two failures were what I based on the Lucus Generator & Control Box document and Generator Test 1, that specifies 2-4 Volts with leads detached from the generator and the engine at approx 3000 RPM (my results were 0-zolts). This test was conducted based on the darn smell that has emitted from the generator after obtaining highway speeds, and the ignition light coming on during this smell at highway speed.

Your notes on the regulator are very interesting. By the way I have the earlier model on mine (the 2-relay model with posts AAFDE). Is this regulator interchangeable with the 3-relay type? What has been nagging at me is what root cause causes a generator failure at high RPM (yes I will test further to first assure that the generator has failed)? Your note on the contact opening at 13.5V does in fact sound like a possible cause. On the model of regulator I have it looks to me like the top contact and one which I did accidentally touch why trouble shooting. After that the armature of it still opened and closed upon engine ignition so I assumed it was still functional. If my regulator were interchangeable with the 3-relay type my local automotive electrical shop has a new 3-relay in stock.

I will do a continuity test on the wiring, I should have known better and performed that first. I’ve been waiting for my MGB since I was about three-years-old so logic is out the window at times, as I just want to drive it before the snow hits.

David, I’ll send you an e-mail and would appreciate detail on polarizing the components. Sending a relay to Bob sounds like a good winter project; I would hope I can get myself functional and converting to solid-state would be a reliability improvement. Once I get myself through this I plan on enjoying it until winter, when I will the put it in the garage, and change to negative ground, convert to an alternator, and upgrade the wiring to Advance Auto Wire https://www.advanceautowire.com/ .

Once again thanks for the detail and I’ll keep you all informed.

Cheers,

Tim

 

[DrEntropy]

I’ve been waiting for my MGB since I was about three-years-old so logic is out the window at times, as I just want to drive it before the snow hits.

A very common malady, Tim!
Congrats on the fulfilment of the desire. And welcome to the Forum.

 

[Tim_Cressman]

The British wife came 20-years ago, so I'm still not certain what took so long for the MG? I consider them both a good find but both being the same age one runs better than the other; puzzling isn't it?

 

[Bugeye58]

Tim, I hope the <u>wife</u> doesn't have charging problems! /bcforum/images/%%GRAEMLIN_URL%%/grin.gif
Welcome,
Jeff

 

[Nunyas]

Tim, I hope the <u>wife</u> doesn't have charging problems! /bcforum/images/%%GRAEMLIN_URL%%/grin.gif
Welcome,
Jeff

hmmmm... well, I guess that would depend on your definition of "charging problems". I would say that if her charging system works too good you could end up in deep doo doo before ya know it! /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

 

[jlaird]

Star Auto Electric Company

https://www.starautoelectric.com/Technical.htm


Instruction on how to polarize a Generator:


In all the years I have been in business, I have heard many versions on how to polarize a generator and voltage regulator. Some versions are correct, others are totally wrong.
Polarization is a procedure which matches the polarity for the generator and the voltage regulator. The majority of the vehicles are manufactured negative ground although some of the older vehicles were manufactured positive ground. The generator has to be set up for either polarity. The generator will charge either way, however the voltage regulator has only one polarity. Whenever the battery is disconnected from the vehicle for any reason the polarization procedure should be performed.
The recommendation on how to polarize a charging system is the following: After the installation of a battery, generator or voltage regulator follow these procedures. The terminals on the voltage regulator are labeled with letters and this is where you will do the polarizing procedure. Both of the components will have battery power so do not start the vehicle or turn on the ignition switch before polarizing them. You will need a small piece of wire fourteen or sixteen gauge with alligator clips on the ends. Find the "B" terminal on the regulator and attach one of the alligator clips, find the "D" terminal and touch the terminal with the other alligator clip. You can touch the terminals a few times and it will produce a soft light spark. Under no circumstances touch the "F" terminal or any other part of the regulator or you could damage the regulator.
For the Lucas voltage regulators that have the teminals labeled A1, A, F, D, E, the polarization procedure is the same however the terminals that will be used are the "D" terminal and either the "A" or "A1" depending on which teminal is used on the vehicle. Either terminal can be used if wires are going to both terminals.
Start the vehicle and you should see the red generator light go off on the instrument panel, you may have to rev the engine up a few RPM, generators have a tendency not to charge at idle speed. If you have a gauge on the instrument panel the gauge will respond accordingly.
Look for more technical information in the future on these page.

Sincerely,
Mike Martinez

 

[Tim_Cressman]

Thanks for the information folks. I’ve thrown in the towel somewhat and converted over to negative ground and picked up a Lucus alternator at the Bronte British Car Show on the weekend. Hated to do this without actually determining the root cause of the generator failures but a least it removes the two most probable components. Continuity test were favorable with the one exception of the now positive lead from battery to starter solenoid of which I really never tested (test leads to short). I think I’ll replace this for kicks very soon.

BTW wife charges fine, I think Lucus could have learnt something from her.

Cheers,

Tim

 

[glemon]

Star Auto Electric Company

https://www.starautoelectric.com/Technical.htm


Instruction on how to polarize a Generator:


...Whenever the battery is disconnected from the vehicle for any reason the polarization procedure should be performed...

Sincerely,
Mike Martinez

I have never read that one before, and I have certainly not followed it, battery gets disconnected many times for work on the car, never had polarized a generator after, never had a problem that I am aware of related to not doing it.