This is my wifes 2003 Yukon XL. The lights dim out and the volt gauge drops along with the blower motor dieing down . The volt gauge actually drops from 14 down to about 10 volts.It will just go up and down while driving. I have replaced the battery and the alternator and it still does it. this thing is driving me nuts. I have checked all the grounds and everything is clean and tight. I work with a guy with a 2002 chevy truck and his is doing the same thing so this has to have happened to someone else. Thanks in advance for the help.I have also checked for codes and it all passes. The battery light does not come on either when this happens.

 

I have gotten two new defective alternators in the past. I have also found a truck with poor ground where it would run but all the electrical was dim and flickered slightly when running. I have had a bad battery cable that looked good visually but nearly broken in half inside the insulation. I have had a bad ignition switch from too many keys swinging on it. I have had a rodent do a sleep-over in the engine bay and chew harness wires (from experience don't tell your wife her car has rats unless you want to buy her a new one). I have had alarm wires tied into the ignition under the dash with chaffed insulation due to coming into contact with metal brackets over time.

I would re-check what you think is good (esp. alternator). Then start diagnostics like pull the positive cable off the battery and put a check light on it to make sure you are not significantly shorting out and chasing fuse by fuse if you find something. Turn off everything possible in vehicle when running including pulling fuses to isolate the problem. I have used a heavy home-made ground cable (modified jumper cable) to run-over the same grounding routes one-by-one to help verify the problems were not in the ground strap/wires.

Good luck.

 

Adding to Chavette's list, I was helping a guy diagnose a no-charge situation, and we were sure it was the alternator. I removed the rubber cover from the output cable, and it was the only thing holding the wire on.

 

Alright,thanks for all the ideas. I will double check the wiring for the remote start and go over the wiring with a fine tooth comb to see if I can find anything. It definitely acts like the alternator but since I just put a new one on and it has the ecu that tells it to charge it throw me for a loop. thanks again.