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MG MGA - Weird little problem

I installed an alternator conversion over the summer.

Fantastic and I am quite pleased with the result.

There is however one little oddity. When I turn the car off the ignition light stays on for quite a while afterwards; maybe as long as an hour.

Alternatively after I've shut down the car and the ignition light stays on I can pull the headlights switch out and back in and the ignition light goes right out.

I've been over the wiring several times and would attest that its done per the book.

I'm going to guess it has something to do with the regulator. Thoughts?

And yes I know the regulator isn't necessary any more but I'm thinking I want to leave it in if I choose to sell the car in the future....that way I don't have to convince a future buyer that everything is indeed OK.
T McCarthy

Tim,
Whose alternator installation instructions did you use? The Moss kit I used provides instuctions to bypass the actual regulator function, while leaving the regulator in place. I think those instructions are available on line. It becomes, in effect, just a connector but remains in place on the firewall. This requires swapping a few wires around. I followed these directions and it works great. You might want to re-check that you did this correctly.
Cheers,
GTF
G T Foster

GT, those are the instructions.

Because the regulator is not truly bypassed in this set up I suspect it has to do with the cut in, cut out setting in the regulator.

Thanks,

Tysen
T McCarthy

I sounds like a capacitor gradually discharging - have you a suppressing capacitor still left on the generator? cheers Cam
Cam Cunningham

Cam,

You are right about the analogy. But no there is no capacitor.

If I understand the regulator construction, it appears that its ability to switch on and switch off is in effect a capacitor function.

I'm wondering if that is what's creating the issue.

Tysen
T McCarthy

Tysen

I have of occasions had the same happen to me with my alternator. I followed the Moss instructions, also I believe Barney's notes on the topic. I too have kept the regulator box in situ, purely for looks and as a convenient junction box for the alternator wiring. I have often heard a distinct click from the bulkhead area when the ignition light finally goes out and have asked myself the question why, but never given myself a satisfactory answer.

I always totally isolate my electrics whenever I get out of the car, so the hour rule has never been an issue with me. When I put the isolator back live, all is ok.

Steve
Steve Gyles

Steve,

That is exactly the same problem.

I think it has something to do with adustments for cut it and cut out.

For whatever reason after the motor stops the regulator is still set to draw power from the alternator....which of course keeps the ignition light on.

I think I have to adjust the alternator cut out.
T McCarthy

Tysen

As you say, a weird little problem. The regulator is out of the loop though. Should be no current going through it. All that is used is one of the terminal posts as a convenient circuit connector, so should not have anything to do with it. All the workings are in the alternator.

My alternator and ignition warning light have been behaving perfectly recently........

Steve
Steve Gyles

Steve, Here it is from Moss.

I'm going to check the cut out:

ello Tysen.

In the original set-up, power flowed from the key, through he lamp on the dash, and then to the D terminal on the regulator.
That same D terminal was shared by the output cable coming from the generator.

When you first turned the key on, but didn't start the engine, the current would flow from the key, through the lamp, to the D terminal, and then to the generator.
The flowing current caused the lamp to glow.

When the engine started and the generator was making electricity, the generator and the batter had the same amount of voltage.
No power flowed through he lamp because the battery and the generator were equal in voltage.
The lamp didn't glow.

Now, you have the lamp on even with the key off.
Current can't flow from the key through the lamp, and to the D terminal.
That means current is flowing from the D terminal backwards through the lamp and to the key.
Because current is flowing, the lamp glows.
If you leave it like that for a day or two it will likely drain the battery.

If your control box (a.k.a. voltage regulator) was not functioning as it should before you did the conversion, you probably have a sticky cut-out relay inside the control box. Opening it and cleaning the contacts will solve the problem.

If the control box was functioning as it should before the conversion, the problem is likely the way the conversion was wired in to mate with the existing control box.

Nobody wants me to tell them this, but in the vast majority of the cases I've dealt with, the directions were not quite followed to the letter.
Since this is a job very few people have done more than once, it is usually a challenge, and something new, to the installer.

My suggestion would be to try to understand why the light is on as I've outlined above, and then look at the installation to be absolutely sure the installation was done as it should be.

T McCarthy

This thread was discussed between 08/10/2007 and 11/10/2007

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