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Headlight switch activates ignition system, truck wont shut off

Hi, I have a 2001 Freightliner Century. When I turn on the headlights it activates the ignition system, meaning the gauges sweep, the idiot lights come on and the fan clutch is charged. With the lights off and you turn the ignition to on the dash lights come on but not the headlights. If I take the dimmer switch and move it up and down with just the headlights on it activates the menu on the computer readout on the dash. The dimmer does dim the dash lights and if I put it all the way down the dash computer goes out as well. The dash computer I'm referring to is the one right above the tach and spedo. I do have 2 active faults. Wheel sensor axle 1 and outside air temp. I didn't think these had anything to do with the issue I'm having with the headlight switch and I'm taking it to a shop for the ABS wheel sensor fault. I'd like to tackle this light problem myself if I can.

I just went out and hit the light switch this morning. It didn't sweep the gauges so I got excited. Started the truck and let it warm up, shut the key switch off and it kept running until I shut off the headlights. Now I know I have a big issue. I was told by a buddy to pull all the fuses and relays out of the fuse panel and check for corrosion. I did that and didn't find anything particularly wrong with that panel.

This truck has had the dash panels stripped off of it and replaced. I've also replaced the gauge cluster. I have removed the gauge cluster from the system and the same problem exists. I repaired corroded wires on the passenger side down by the threshold. I have know idea what they are for but one wire was corroded out of both sides of the connector. I have repaired the main body ground on the drivers side down by the tilt switch. I know I have to be back feeding from somewhere but I have no idea where to start isolating systems out of the circuit.

Any help would be greatly appreciated since I'm also dealing with another truck with a similar issue.

Answer this question I have this problem too

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According to the witing diagram the power to the igntion relay only comes from the key switch directly. So they must be rubbing together with the light switch wiring either under the dash or right by the fuse panel.

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Thanks Allan, I'll check through again. Someone told me to check the low voltage cut off switch. Could that be a possibility?

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Kerry will be eternally grateful.
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