I think its a 1997 . I got to work and one of the drivers said his low beams were on and wouldnt turn off. No other lights were on . It has a left and right low beam fuse. I pulled the left and it went out but pulling the right didnt do anything. I pulled the relays that didnt do anything. I unplugged the switch they stayed on . I decided to drive it to the shop someone watching said they went off a couple times then stayed off on the way to the shop? I dont know if it had daytime running lights or not. I pulled it in the shop and charged the bats and turned the lights on and off several times and they stayed off.
Try the signal dimer.
Feed back through driving lights if it has any?
I unplugged it and they stayed on. I dont know if it had them The driver said it didnt . I wish i had the original owners manual.
If they are constant power earth switched circuit you may have a short to ground in wiring. If positive switched, (still had power after pulling fuses) my guess is a short in harness to a power source.
If it's back on i am going to give the wiring a going over. I was moving it into the shop to do that when they went off.
The driver went to use it today and the lights came back on while he was fueling up but when he moved it agin they went out. I will look it over agin when they don't need it.
I got a call from another driver about 5:30 that the truck was parked and lights were on . I bet the driver didnt check when he park it. I told them to pull the bat cable for the night.
I found out yesterday that if i opened the hood and shock it back and forth the lights would come on and off by themselves . This would make you think it was were the hood hinged or close by but i shock and pulled on the wiring till i found it must be close to the starter. I cut harness open moved stuff around and they stopped coming on . I ran out of time . They are going to use it today and i dont know when i can look at it agin. What was funny is one harness labeled Engine harness seemed to be something to do with it . the tubing around it was backed full of dirt i opened it up cleaned the dirt out and couldnt make the lights come on agin by them selfs. They work using the switch great.
I found the problem the wiring harness runs over the top of the starter, The harness covering wore through on the hot cable on top of the solenoid then it wore a spot through the yellow wire to the head lights.
Nice find Doug!
What's good is he reasoned it had to be shorting to a constant power source, and like all it seems these day's, the manufactures run all the harnesses right next to the starter.
It seems there should be a better way or place to run the harnesses but maybe not.