2.4L Charge Light
I've had my '89 D50 4x4 with a '92 2.4L efi in it for awhile now, running beautifully after a rebuild about a year ago. I recently changed the stock alternator out to a 75 amp bolt in unit from a 1990 mitsu van and have had no issues, however the other day my charge light came on very dim at idle, increased the rpm a little and it went away, it's been doing this on and off until today finally the radio and the instruments died as well as the fuel pump without showing the charge light, and obviously causing it to shut down. I checked all connections on the charge circuit that would trigger a charge light and all engine connections and found nothing out of place. Eventually it started up again with a half-lit charge light, still varying brightness with engine RPM (higher RPM gets dimmer, brighter at idle) and my aftermarket tach was jumping all over the place. On the drawings all that I can find that would effect the charge system would be the fuses (they're fine), ignition switch, voltage regulator/alternator, or possibly the coil... Anyone have any ideas where I should start or anything I may have missed?
Tach jumping is getting intermittent power to coil since tach runs off coil signals. While car is running if you put headlights on are they dim? Put a volt meter on battery and make sure you have about 12.6v on battery. I think the alternator on that year had internal regulator, so if it is going bad you'll probably have to replace alt too. DO you have a spare alternator around? try switching out and see if that fixes it. That intermittent stuff reminds me of a voltage regulator going out. Have the alternator checked at a local auto parts store , like Autozone or O'rielly's, it's free. They check batteries also. Coils usually just burn out, but very rarely. Make sure engine is grounded to frame real well from battery post, NEG.
When running it should show 13+ volt to a full charge of 14.2 volt at the battery. The charge light problem might be because the regulator is taking a dump. That will be confirmed with the volt test. On many systems the light is needed to make the regulator kick in. Some need to reach a cretin RPM to kick in. IDK about yours if thats how it works or not. Then there is the current draw needed to shut off the light. On my build truck I used a LED and it glows because the amount of voltage to make it light up is only 3.5 volt. The regulator makes a ground to light it up. But the LED does not draw enough to completely go out.
Our suspicions have been confirmed, Voltage regulator is no good. Luckily the alternator is still under warranty!