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MG MGA - ignition light

As I was leaving the MGCC meeting last night(following Vin's fan belt squealing MGA out of the car park) I noticed that my ignition light was glowing faintly. It would sometimes go off, then glow again intermittently all the way home, 20 miles or so.
It was never fully illuminated at any time and when I got home I switched the engine off the lamp turned off as it should.
When I restarted the engine the ign light went off as it should and seemed to be back to normal.

Has anyone else ever experienced this?

My car was fitted with a lucas alternator last year and this has worked fine.
I used the original voltage regulator as a connection block for the alternator wiring, disabling the internal coils and contacts by using thin plastic strips between all the contact inside the regulator.

This may be the first time I have noticed the slight glowing of the ign lamp as it was only very faint and also it is the first time I have driven the car with the headlamps on since fitting the alternator.

Has anyone any ideas?
Should I be worried about frying my electrical system etc?

Colyn
Colyn Firth

The instrument should have a light shield tube around the ignition indicator bulb. If the tube is missing or partly out of position it could allow the illumination lamp light to get to the jewel and make it glow a little when the lights are on.
Barney Gaylord

Colyn,
I installed an alternator about 2 years ago. It came from Moss and I followed their directions to the letter. When I first fired it up I too had slight (and sometimes more that slight) glowing of the ignition light. After checking the system to determine it was charging properly I discovered a set of contacts inside the requlator that were somehow being pulled closed, causing the light. I'm guessing some type of back EMF thru the associated coil. (I left the regulator in place, even though with the alternator it was just a junction box). As I recall, I put a piece of electrical tape between those contacts and solved the problem. The system has since work flawlessly for thousands of miles.
Cheers,
Gerry
G T Foster

Thanks Gerry, I had a problem when I first fitted the alternator with the ignition light staying on even though the ign was switched off!
Like you I had used the regulator as a connector block but I realised that the regulator was still partially operating and causing one of the coils to trip.
I used some very thin plastic strips between the points to insulate them which solved the problem.

I had better take the cover off to see if any of them have slipped out of place.
Will let you know how it goes.
Colyn
Colyn Firth

Colyn. It could be that over time your thin plastic strips have got thinner due to conduction/sparking through the plastic. Best idea would be to replace the strips anyway and then see if that helps.
Neil
Neil Purves

I just had my alternator checked out by a very good auto electrician who is familiar with generator to alternator conversions.
He was happy with my re-wiring and said that the alternator was charging exactly as it should.

Apparently the ignition light is prone to this very faint intermittent glow when wired up using Barney's alternator wiring method. It is not due to the original ( but now redundant) regulator partially operating. It has something more to do with the alternators built-in voltage regulator being slightly affected by the mga ignition circuit. ( sorry I cant be tecnical than this, I will try to learn more.)

At least it means that the re-wire for the alternator that I thought was urgent can now wait for winter now.

Colyn
Colyn Firth

The light reflects the balance between Alt voltage and IGN voltage, so any V drop between the mutual connection point and the light on the IGN circuit will cause this. If your car has not been thoroughly gone over so far as all connections and switches are concerned, you might easily expect a couple of volts drop. I've found as much as 3 or 4 V. Measure the V across the lamp, it <should> be zero.
None of this has anything to do with MGA in particular, but it may partly result from the multiple connections around the old regulator.

FRM
Fletcher R Millmore

Thanks Fletcher
that sounds a very similar, but a very much more understandable, answer to the one given to me by the auto-electrician that I took the car to.

I actually get it now.

I will check over the connections on the ign switch circuit, on the regulator block and also put my digital meter across the ign light to see if there is any voltage there.

I intend to completely bypass the old regulator in the near future and also fit a much heavier gauge output wire from the alternator to the battery.

The present set up is as suggested on Barney's site
with an extra yellow wire from the alternator to help cope with the higher output from it.

Thanks again Fletcher

Colyn
Colyn Firth

This thread was discussed between 24/06/2010 and 10/07/2010

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