1997 kw t600 voltage drop problem

hey guys,

i got a 1997 t 600 that has developed a problem. when you turn on the instrument panel lights the voltage drops down. if you turn the dimmer switch all the way off it goes back to normal. But if you slowly turn up th light intensity you can watch the voltage drop. i thought it might be the switch, so i unplugged the pigtail going to the rotory switch and used a jumper wire to put power to the light circuits and it still dropped. any ideas. the only other thing that has happened is the blower motor switch for the cab hvac got hot and melted part of the plug but it still works. I did notice that the blower motor switch gets hot when the fan is on high but is cool to the touch on any other level. is it possible for the blower motors high setting to be causing a draw through the ground with the panel lights? i have also been looking for burned bulbs but havent found any. Some of the panel switch lights are not working but unplugging the ones that do not light of didnt change anything. it doesnt seem to be a direct short just a big draw on the panel lights

 

i am going to replace the switch to the blower motor but it looks like to me that the power wire goes direct to lights and the intensity is controlled by anount of ground it recieves. i hooked my circuit tester to the center wire of the light socket for the hvac control panel and then tested the five wires going to the switch all but one made the light light up and one was controlled by the dimmer switch it was a heavier white wire with a smaller wire in the same plug socket the little wire run to the light socket that i was using to test with. so now i am wondering where that heavier white wire runs to. i could really use a electrical diagram. it is nice that paccar has little labels attached to most of the wires tell you what the are and there are lots of battery power wires ready behind the dash to connect things too.

 

i would love to get my hands on a wiring diagram for this truck. i am going to mess with this some more today i will update later. i was glad it wasnt the riostat dimmer switch, kenworth wanted 130 bucks for that.

 

thanks for the link but
not sure i want to spend 30 bucks to see if they have one

 

thanks kwcam, i check the main ground on the firewall. i wouldnt have even seen it if you hadn't told me about it.

I did find my problem tonight. it is the voltmeter panel light. not the bulb but if you leave the bulb and socket out it doesnt drop voltage at all, if you install it it drops even switching bulb sockets didnt keep it from doing it so it must be somewhere at that gauge. all the other lights are working fine except that one. it is in thetop left hole of the panel by the drivers door above the ignition switch. the bulb just slips in then turns a little to lock. not sure how it can be grounding out but it seems to be the problem