05 Duramax Electrical issue
 

My buddy has an 05 Duramax that began acting akward today. He noticed the instrument cluster gauges started acting odd, the gear selector would not show the underlining of the gear he was in, the voltage meter was reading down at 9 volts, and when he parked the truck the gauge lights did not want to turn off and neither did his radio. We took the truck and had the alternator tested and it checked out fine. The Driver side battery tested bad so we replaced it and had the same result. The battery that we installed was straight off the racks and we did not charge it yet, we are still experiencing the same propblems. Has anyone had the same problem or know what this could be? He also had the truck smogged recently so we werent sure of the possibility of this stemming from something being plugged into the computer for the smog test. The truck is completley stock other than an exhaust and cold air intake. Any input would be great.

Got it figured out, the previus owner installed an aftremarket head unit and there is a power module that had to be run to the head unit to power it due to the stock harness not being able to power the aftermarket unit. since the power module went jay wire it cause issues in the displays for some reason.

Head unit huh, makes since, chevy runs everything thru the head unit. if the gage prob comes back, its a step motor though. 3 of my gages work when ever they feel like it. i could be crusieing down the high way and watch my RPM gage go from 2000 don to -1000 its freaky for a sec then you realize that you are still running at the same speed and RPM. then its just a waste of a o shit moment