I have a 97 f350 cclb drw. When I turn on the headlights they will not go off unless I unhook the battery cables or pull the #4 relay. They will dim when I push in the switch and the headlights go off but, all of the marker lights will stay on. I have replaced the switch and the #4 relay neither one fixed the problem or made any difference. Can someone figure this one out?

 

Would the truck happen to have a JVC aftermarket radio in it? My '94 F250 IDI would do something similar to this at times if the radio was on. Turn the radio off before the lights and all was well.

 

My radio has been off because I have been having to unhook the battery cables I haven't turned it back on i do have a aftermarket radio but its not a jvc and I've had it since before Christmas and this just started a month or 2 ago so I don't think it would be the stereo.

 

Just a thought. On thinking back my truck was a little different. If you had the lights on, radio playing and engine running, you had to turn the radio off first or the engine wouldn't die! A friend had a gasser F150 with the same radio and his did the same thing.

 

How's the wiring look where the switch plugs in? Same for the power distribution box, has something (water) gotten in there to perhaps short something out? Sounds like you've got crosstalk over two wires somewhere.