Ok, the lights in the HVAV control unit didn't work when I got my truck. Found all 3 bulbs burnt out, replaced, not 2 hours later they stopped working again. Took it apart to find the plastic housing the bulbs mount in melted on all 3 bulbs. Truck runs a consistent 15.5v even with all the lights on, done tis since I got it. Has anybody else had this problem before and if so what fix did you come up with? Same truck as in sig..

 

check and clean all battery clamps, u probably have some corroded somewhere, pay particular attention to the cross over cable , on these trucks the right battery is charged by the alternator, the left battery is charged by the cross over cable, this is likely a cause for the 15.5 charge, "loose or dirty connections", good luck ;;;;

 

I checked and cleaned every gound I could find also did the positive cables as well, When started cold, it'll run about 12.5v for about a minute then jumps up to between 14.5v and as high as 16.1 according to my scan tool. I know its not the grid heaters because I can hear and see them cycle by the way the lights still dim. It almost acts like a lazy alternator when you first start it and have to wait for it to wake up. Once its awake, you cant bog the alt. down with anything the truck came factory with(ie..blower motor on high, all the lights on w/high beams, mirror heaters, 4-way flashers...)even add the aftermarket stuff like key up my cb w/2500 watt kicker, jumper cables hooked to my wifes dead durango, 30ft stock trailer w/more chicken lights than a chicken hauler, it still stays right at that 15v mark. My big problem is it keeps melting the little plastic like mounts the bulbs are made into for the HVAC control head. The alternator is an OEM unit, 136amps.
Just geting tired of turning on the overhead lights while driving down the road to adjust the a/c or heat.....

 

Check the voltage on both batteries, engine off static reading. now start truck measure voltage at both batteries, as the right battery charges the left battery by bleed across, no alternator charge directly at the left, it is like hooking jumper cables, it takes a while, I drive 20 minutes as the voltage settles down to 14.5 or so,

 

Once the alternator wakes up, it don't move for as long as the truck runs. This is how mine will read all day...16v read by the scan tool 14.8ishv by the ecm

 

Ever figure out the high voltage issue???

 

No, never did and it doesn't seem to be causing any issues.