Charge light is on, but alternator still charges!

[ytt105]

Drove from Canberra to Woolongong yesterday to pick up a cub camper in my 93 Rangie 3.9l EFI with gas.

Yesterday near Goulburn, about 100ks from Canberra, the charge light suddenly came on.

I pulled over, everything looked good, I checked the charge rate with my multimetre and it was 13.8 - 14 volts.

So I disconnected the second battery so as to have a reserve if it was having problems and then drove to Wollongong and returned, (about 600kms) towing an offroad cub camper, in the rain, at night, with the charge light glowing brightly the whole way.

What gives, where is my problem. By the way it is a Magnetti Marelli alternator with over 250,000 kms on it.

[THE 109]

sounds like there's power from another cable or component on that circuit,maybe from 2 cables rubbing together(short circuit I think).Thats what comes to mind,hope it helps.

[ytt105]

I thought so too but there doesn't seemd to be any spurios earth as when the wire is disconnected from the alternator the light goes out.

[Woop]

I'm not familiar Magneta Marelli type Alternator, but it might be: Faulty exciter diodes or worn brushes--although bad exciter diodes normally make the lamp glow dimly.

Nick

[THE 109]

My guess is something inside the alternater has busted,might be time to replace it or get it checked out.

[Philip A]

Just having a think about it, the charge light measures the difference between the voltage at the battery/starter and at the alternator, via the ignition switch.
If you have 13.8 volts at the d+ terminal of the alternator, then it would seem that there must be a short circuit to earth, between the ignition switch and battery/starter . If it were between the light and the alternator , the wire would burn. if between the light and ignition switch it would be on all the time regardless of whether the ignition was on or off.
My recommendation is to look at the small wires that come off the starter solonoid, and see if the ign light one has fallen off and is earthing. If the light does not source from the solonoid, see where it does source and trace it back.

Do I get a prize if I am correct.
Regards Philip A

[justinC]

I have had a faulty regulator cause this problem, I think there is a warning lamp circuit as part of the IC reg, and even though the alternator will probably continue to charge, the lamp will not go out.
As far as I can remember, all that was done was the reg and it fixed it.

JC

[justinC]

I have had a faulty regulator cause this problem, I think there is a warning lamp circuit as part of the IC reg, and even though the alternator will probably continue to charge, the lamp will not go out.
As far as I can remember, all that was done was the reg and it fixed it.

JC