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MG Midget and Sprite Technical - Alt conversion ignition light

I installed an Alternator conversion kit from Moss a couple of years ago in my 1971 midget. The kit uses most of the control box connectors and I found that originally, the ignition light would remain lit with the control box grounded. Disconnecting the black wire to the control box left the warning light functioning properly.

Now the light glows at half brightness but the alternator charges perfectly. I have considered rewiring the warning light circuit to bypass the control box altogether but wonder if it isn't bad diodes or some other alternator fault.

I have not experienced any battery discharge and have been driving the car this way for months. It is bothersome, especially at night, to have a red light on.

Any suggestions would be appreciated.
Glenn Mallory

Hi Glenn, sounds like there may be some wiring issues, but if you are happy with the way everything works, you could do what i did... this will make the light work ok.. but its fixing the symptom rather than the cause..

I fitted a set of LED warning lights when i rewired my car, but i found that the battery light was always on even though the alternator was working fine and no issues with the battery, what i did was solder a small resistor(try a 50 ohm, 2 watt) in line with the bulb holder. This made the LED have a similar resistance to a bulb and now it works ok.

You could try the same thing, it only costs pennies.
But like i said, as you are using a bulb anyway i suspect there are other issues underlying the problem.
Andy Phillips (frankenfrog)

Hi Glenn,

It's normal practice to remove the old control box alltogether. Then join all the thick brown wires together and insulate. Ignore the earth , it's not needed. Finally join the thin browns (brown/yellow and/or brown/green) and insulate, this is the warning lamp circuit.

If the warning lamp still glows, disconnect the plug from the alternator, if it stops doing it, the alternator is faulty.
SR Smith 1

Glenn, by control box do you mean "Voltage regulator"?
I would have thought that the new alternator conversion would have negated the need for this altogether as the alternator should have inbuilt regulation. Just a thought.
R W Bowers

I fitted an alternator to my car using the instructions here...

although I did change the thickness of one of the alt wires - there's a thread on here somewhere about it.

Had no problems whatsoever.
graeme jackson

Thank you. I will try connecting the ignition light directly to the alternator small wire. I agree that there is no place for the external voltage regulator in the circuit and was surprised that Moss instructed keeping it in the circuit. Probably to use existing wiring and connectors.
Glenn Mallory

I did exactly what SR says and it works perfectly. I used a terminal box from B&Q hardware stores, but I' m thinking about pulling the guts out of the old control box an using that to make it look more authentic.

b higginson

My wires are in connector blocks wrapped in tape. Been that way for at least 30 years. Very dirty now, but no alt problems.
Lawrence Slater

This thread was discussed on 14/05/2013

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