Ignition light not working

An alternator warning light works by:

The bulb is powered by the ignition switch, the earth side of the bulb goes to the warning light terminal on the alternator.

So check your wiring.

mrcheerful

My first alternator factory equipped car - a '69 Rover 3500 - had an alternator warning light 'relay' which looked like an old fashioned flasher unit, ie an aluminium tube with a bracket on the end. Think the label on it was green. The alternator also had an external regulator mounted inside the car.

Sure its charging ? Had similar on a Viva (AC Delco alternator). One of the flyleads on one of the brushes had parted company. The wiring for the light goes though the brushes (or did in this case), and hence it never came on, either at startup or once running.

The only indication was - after a surprisingly long last run, and I've no idea before that when it parted - the guages started to drop (fuel / temp) and eventually the car misfired and died.

Couple of quid to get new brushes, and three hours to get the sodding alternator back together (Haynes said "We recommend you don't take this apart", really useful to read when its in bits on the kitchen table ...)

Thanks for responses, it gives me a few things to look at.

Cheers John

Lucas ACR (17 ?) alternator,AFAIR, so if the light isn't working, then the alternator can't charge -- the bulb is itself a component of the charge circuit and must also be of the correct wattage rating. It's usually in a red clip-in holder to identify it, not the usual black. An incorrect bulb may itself be enough to cause the problem.

Any English electrical diagnostic manual of the period ought to explain how to test it, although a real alternator test set is helpful and the usual fix is just an exchange alternator anyway. Usually they fail in a close-run race between brush wear and the rectifiers failing. Rectifiers are easily checked over with a multimeter. If you do have a

40 year old alternatior in bits, then change the bearings too - maybe even the sliprings. Fortunately these things are common as muck and easily sorted out.

Oh, and you have checked the fanbelt first ? 8-)

I doubt this very much. I have use Lucas AVR alternators (16s I believe). On my Jem the ignition light isn't working at the moment but the alternator still charges and doesn't go over voltage. In any case the light comes on when the battery is discharging, not when it's charging. It must be connected to a diode bridge inside the regulator.

It's possible that the lamp circuit is used in the first instance to excite the alternator, but as soon as there's some residual magnetism it will start generating without any assistance. I've noticed a slight delay before it kicks into full charge after starting.

If having checked the bulb, all the wiring (the lamp is wired between the alternator warning light terminal and ignition +ve) and the connections inside the alternator it still doesn't work then try replacing the regulator pack. They are obtainable separately despite what some suppliers tell you.

I had an alternator like that. A few weeks later, it started to overcharge intermittently, which became obvious at light when the headlamps would suddenly flash a lot brighter. This gradually got worse until it blew a headlamp and tail light bulb. At which point, I decided it was getting expensive and needed fixing.

A new regulator (ask in an autoelectricians - you can buy them as a replacement part) fixed it completely.

Jim