2001 Freightliner Century Head light switch activates ignition and gauge sweep.

Hi guys, I think I have a weird one here.

On my Century when I turn on the headlights they work but it also activates the ignition. Meaning that the fan clutch is charged, the guages sweep and idiot lights come on just as if you turned on the ignition. Also with the lights off when I turn the ignition on my dash lights come on only. No headlights with the ignition switch. Could this be the dimmer switch?

Any help would be greatly appreciated.

 

I found wiring on the passenger side threshold that was corroded out of the connector. Fixed them this morning. Then I was fooling with the light switch. It didn't sweep the guages so I started the truck and let it run for a few minutes and went to shut it off. It kept running until I shut off the lights. After I shut them off and the engine died I flipped them back on and the gauges did their sweep and the idiot lights came on.

I really hate electrical problems. The only thing that doesn't work electrically is the Recirc/Fresh air switch on the heater control. Other than that everything works.

I'll pull all the fuses and relays out of the fuse panel in front of the passenger and behind the driver today and report what I find.

Thanks for the replies.

 

No corrosion going on in the fuse box in front of the passenger. Now to check behind the drivers seat, AFTER I fix the main ground on the driver's side floor. Just fount that 3 wires on that ground were corroded badly.

 

With only the lights on and messing with the dimmer switch when the dimmer is off the dash readout barely displays, no dash lights, no idiot lights and the fan isn't charged. Move the dimmer switch up and everything starts to go haywire. Idiot lights come on, gauges sweep, fan charges and dash display lights up. If I move the dimmer switch fast the dash display will run through all the options.

I'm going to get a new dimmer switch tomorrow. Yes I'm chasing parts. I have already tried a different headlight and interrupt switch. Those didn't change anything. Also when I'm playing with the dimmer the Trl Marker light relay clicks.

 

Disconnected gauge cluster, no change. Same as with.