I have a 97jgc with the 4.0L. The problem is when all the accesories are turned on the alternator doesn't charge. When running the alt is charging at 14.01 volts with no accesories turned on. When I turn on the a/c, lights, heater, etc. the voltage drops slowly to 12.56. While driving down the road the alt gauge bounces back and forth between 12 and 14 volts sometimes. I have installed two new alternators and a new battery. All the grounds have been cleaned, the cable connections are clean, the alternator is getting 12 volts to it, and the belt is tight, all the fuses are good. I tried wiggling wires with no success. If I raise the idle when its not charging the voltage goes up. Opened up the wire looms and found no broken or corroded :banghead: wires. Please help me out on this one.

what kind of amps is this thing putting out?12 volts with all the accessories on doesnt sound out of line. especially at idle and esp.if the voltage goes up with rpms.

I don't have an amp guage unfortunately but I have done many alternators and checked many charging problems and have never had this problem. Even with all the accessories on it should still charge a minimum of 13.5 volts.

is the battery going dead?the volt gauge is not going to give you the full picture.you really need to knowhow many amps the alternator is putting out.by the way that alternator doesnt have its own voltage regulator.that is controlled by the pcm and if there is a charging problem,your check engine light should come on.also the check gauges light should come on.if you dont have the equpment to test it im sure you can find a shop that can test it for you.

The battery is not going dead because it is a new one but eventually it will with the lights and a/c on at the same time. I hooked up my scan tool and checked out the desired voltage in the jeeps computer while it was running and it said 13.5 volts desired, which at idle with no accesories on is what it reads. The desired voltage stays the same when I turn on the accesories but the actual voltagae drops to 12 volts. I toggled the field voltage via my scan tool with the engine off key on, it is working, but when it comes out of the alternator at the other field connector it fluctuates between 12v and 0v. It sounds like a bad alternator again but I can't believe three alternators would have the same problem wrong with them. The wiring seems to be ok no corrosion or damage. I even had another mechanic check it out and they couldn't figure it out either. I understand your point with the amperage but the voltage is not right regardless.

maybe im missing something.are you saying that the problem is that the voltage drops at idle when you turn a bunch of accesories on?What happens if you rev it alittle?every car i have ever seen will do that.an alternator can only put out so much at a given rpm.Alternators put out current and thats measured in amperes so you have to know how many amps its putting out before you can decide if its good or bad.a good alternator typically puts out 100 amps or so but it wont do it at idle.and if the load on the battery is greater than the amount of current that the alternator puts out the system voltage will drop.i agree with you that its hard to believe that 3 alternators could have the same problem.But to be able to diagnose it properly,you have to know how much current the alternator puts out.dropping to 12 volts at idle is not by itself a problem.but if the battery ends up going dead than there is something wrong.by the way, where are these replacement alternators coming from?there has to be a way you can have your alternator tested before its condemmed.i mean if its a bad alternator, its a bad alternator.but 3?i have worked on a lot of jeeps in my lifetime and the only ones that ever had bad alternators where old xjs with gm alternators.the japanese ones are usually very reliable.