Ive had volt problems in my jeep for a while now with this jeep. The stock alternator finally quit a few months ago so I bought a brand new 90 amp, put it in and still the same issues.. Sometimes it will sit at 14 perfectly and never drop even with accessories running, but most times its always under and will drop into the red, even if all i have running is the A/C

recently I put a 117A out of a GC in it, STILL exact same issues..

This is where it sits with just the headlights and blower motor going..

 

try checkin all your connections, batt., alt., especially your grounds.

 

Are you sure you have good battery cables and connections? Are your ground connections clean and corrosion free?

I was curious about my in-dash volt meter showing a drop whenever I turned on the AC, and ESPECIALLY the blower. I was seeing 13.9V at idle with a Fluke 77 DMM, but the in-dash gauge didn't show that high, and with lights and AC it showed noticeably lower. My solution was to install a digital volt meter so I could see more accurate voltages while driving.

http://www.jcwhitney.com/led-digital...wx?filterid=j1

I can now see with the engine running 1500rpm, headlights on high (2x65w), AC on with blower on high, rear window defroster on, auxiliary lights on (2x85w) I'm showing 13.2v, so still charging.

When running the power windows UP and nothing else on except the engine, the voltage will drop below 12V and the meter will flash IF the switch is held in the ON position after the window(s) are up.

You might have an intermittent poor ground, or possibly intermittent short.