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Hello I will help you with your question,
You need to follow the green wire from the alternator through the harness where it runs under the battery tray to the PCM. You have corrosion or a break in this wire. The green wire is used by the PCM to tell the alternator to charge so if there is a break you will have no alternator operation.
By the way it is very bad practice to remove the battery cable from the battery while the engine is running you can damage the PCM/computers.
The other possibility is that the fuseable link from the alternator to the battery is blown so with the cables attached to the battery check the large B+ terminal on the alternator for battery voltage.
Let me know what I can do to help you with this
thats for a 6cyl 4.0?
it is reading like 12.0 on the dash gauge, but like i said it is running completly on Batt.
would that sound more like the green wire or more like the fuseable link?
IT could be either that is why I posted both checks. I would check for battery voltage at the B+ (large) terminal on the alternator first then chase the green wire. Both could be the problem but we see a lot of corroded/broXXXXX XXXXX wires due to the routing to the PCM
ok, one last? Would a new PCM from autozone need to be coded @ the dealer before it would work in my jeep?(i did give them my vin. before ordering).
And what does it mean to have it black keyed? My key has a black top??
If they had your VIN you should be able to plug it in and it should work but it does not sound like the PCM is your issue. Be sure you have a complete piece of green wire between the PCM and the alternator and the B= terminal on the alternator and the battery and you should have charging again.
The keys are coded for the security system. The black key is one type and the grey head is for the other type. The PCM and the SKIM module have to match but with a black key you don't have to worry about that. If you had the wrong PCM it would not start.