Have a 96 XJ showing very low voltage on internal guage. Checking voltage at battery with engine off I get 12.20. With engine on 12.55 and slowly goes up to 12.65. Same reading at back of alternator. Note I had to manually charge battery after jeep would not start a few days ago and have to put it on charge every so often. I did the battery / ground wire upgrade after this happens to at least partially eliminate wiring as the problem.

So I want to test to see if the voltage regulator is bad. I read that you can remove the wires from the back of alternator and then jump one to pos on battery and ground the other. After doing this if I get a higher voltage reading while running it means the regulator is bad.

So this is the wiring I took off back and other are two terminals on back. Which do i jump to battery ?

Additionally two auto stores tested and said regulator had failed. Assuming this is the case, is there a replacement alternator I can get that has a regulator built in so I don't have to install an external one?

 

a '96 is regulated by the PCM, as are most XJ as far as I know

check archives

 

How old is the battery and does it have removable caps to check the cell levels. What condition are the cables? Are the posts and terminals clean and in good shape? And are the terminals properly tightened? Dirty grounds can cause issues as well. The XJ is very fussy about that stuff.

 

Sounds like a bad alternator to me.