12bravo

Rednroll

My only thought would be to install a Big 3 power wire upgrade. Check out youtube if you haven't heard of it, it's pretty common with the audio folks. Quite a few have reported that the stock grounding is kind of weak and have had problems with the starter turning due to it not pulling enough current. I've never had any problems charging or starting on my 2009 JKU but I've installed the big 3 the 1st year I got my JK new because I have a pretty elaborate audio system installed which would dim the head lights on deep bass note hits. Going from memory, I ran an additional 4AWG RED wire from the alternator to the B+ battery terminal, an additional 4AWG black wire from the NEG battery terminal to the interior passenger side fender connection, and from that fender connection to the frame I ran an additional black 4 AWG wire. That should effectively increase the charging capabilities of the battery and increase the ground strength from the Neg terminal to the chassis. I ran these 4AWG wires in parallel with the existing factory wires, which I believe are 8-10 AWG, which when ran in parallel with the added 4 AWG wires provide you a 2 AWG wire charging and grounding system. It's a pretty simple upgrade and one that's worth it, even if it doesn't solve your current problem. My headlights no longer dimmed after doing that upgrade and I haven't had any charging issues over 9 years of ownership.

However, based on your symptoms it sounds like your alternator needs to be replaced. After you start your Jeep, you should be able to remove the B+ connection from the battery and it should continue to run, which is usually a good check to see if your alternator is good/bad.

12bravo

Rednroll

Just saying.

Sequel

I think you are condemning the computer way too fast. Our jeep generators, at least my '14 and i think your 12 has 2 wires coming from the PCM. One is Gen Field Control and one is Gen Sense. The Gen Field Control is a pulse width modulated 12v (really batt voltage). So really you need to validate that signal is occurring from the PCM. An oscilloscope is best as you can see a square wave of 0 then 12v back and forth. Since most people do not have that, you may try a regular voltmeter. it won't be fast enough to see the voltage turning on and off but you should see the meter trying to average a reading or "bouncing" around trying to find a voltage. If you saw 0, that would be an issue.

Sequel

The other tests you should do is a voltage drop test between the alternator battery feed and the battery positive post. Then a voltage drop test between the case of the alternator and battery negative post (not the clamp but the post). Both should read almost 0...like less than ..25 volt. Google the procedure for voltage drop testing. This will allow you to verify if you have good cables and grounds to the alternator.

12bravo

Sequel

That's good. Out of curiosity, what is the voltage reading at the battery with the car running? How about when the engine is at 2k RPM?

12bravo

Sequel

Was the voltage different with the engine running? Or was there do difference between battery voltage with the jeep off and when it's running?