Every Wrangler 91 and newer the voltage regulator is built into the ECM, the computer has complete control over the alternator.
Here is a bit I wrote for a Jeep board on testing the newer style alternators:
--------------------------------------?br>
Don檛 pull the cable off the positive terminal on the battery, this is a bad habit. Alternators need power to create power, so if you remove the power it is possible for an alternator stop charging, and hence the vehicle will die, yet the alternator can still be good. Also pulling the positive cable and replacing it creates weird spikes in the electrical system, which can fry things like your ECM.
With the Jeep running, your voltage should be between 14-14.9 volts. 13.0-15.0 volts is acceptable, but it should be 14 something. If it is 14 volts it檚 a pretty good indication the alternator is fine. Every now and then I檝e come across an alternator that puts out 14 volts, but little to no amps. 14 volts @ 1 amp isn檛 enough power to charge anything, but this isn檛 real common.
If you don檛 have 14 volts, you need to check a few other things. Most all alternators have a wire harness going to them. One of these wires is for the field voltage, if you don檛 get power to the field, your alternator won檛 charge. On newer YJs and all TJs, the voltage regulator is controlled by the ECM. On these alternators there are two wires on the back, one constantly cycles between 10-12 volts to control the alternators output, while the other is a reference wire to tell the ECM how much power the alternator is putting out. On CJs and early YJs the voltage regulator is built into the alternator, so the field wire, will have a constant 12 volts. If you have power to the field, but aren檛 getting 14 volts, it檚 a pretty safe bet your alternator is bad.
If your alternator is putting out 16+ volts, stop driving the Jeep. Either your voltage regulator is bad, or (on newer Jeeps with the ECM controlled alternators) your battery could be bad. I檝e come across several newer Jeeps where the ECM will try and over compensate for a bad battery by boosting alternator output. Last WJ I worked on that did this was spiking to 22 volts!
If all else fails, check with your local autoparts store, almost all of them can test your alternator both on and off the Jeep.
--------------------------------------?br>
You're gonna need a multi-meter for this one, if you aren't familiar with them, check out my writeup here:
http://bbb.quadratec.com/cgi-bin/ultimatChanged the alternator on my 1992 jeep wrangler and battery still not charging. Changed alternator again. HELP
Never fear, the wannabe mechanic is here. or something like that.
OK, grasshopper. When you put in new alternator your battery is supposed to be fully charged or you may burn the new alternator out.
Now if your battery has a weak cell, it may take a charge but then only hold it for an hour or not charge up at all. Apparently with a new alternator you need to get the battery checked out.
Get a Haynes Repair Manual at the local Auto Zone or auto parts store in your area. It will troubleshoot and show you how to fix your vehicle. Also on the Auto Zone site has a section for vehicle maintenance
If you move the belt it should move I think about a 1/2 inch more or less. Also clean the battery posts. If they are dirty this may prevent the battery from charging. Go to the Dollar Store and they have some battery post cleaner brush there for a buck. Just as good as the $5 one at the parts store.
So when you charged the battery did you get it checked out by the auto parts place. If your battery is good, posts clean, alternator new, then you have to check the cables on your starter which may be loose or broken. They are part of the circuit. But get the manual and it will tell you exactly what to do. May the Force be with you.
Go to Auto Zone or other parts store that will check out your vehicle for free. Call first though as only selected stores do this. Light may be from a jillion things from oxygen sensor bad to low oil pressure but something.
