88 volvo 240,
For some reason, my headlights and parking lights don't work together.. when I turn my parking lights on everything works as it should, but as soon as I switch to headlights, my dash and panel lights go out and so do my parking lights.. if I switch back to parking lights my headlights stay on and the parking lights and dash and panel lights come on again. But when I turn off my car and turn the switch completely off my headlights still stay on until I unplug the relay.
I have no idea what the problem could be anymore, I've replaced the switch the relay on the drivers side kick panel and the main relay under the hood and still the same results,

Oh and if I drive with the headlights on in the parking light setting, after about 15 or 20 minutes the headlight will turn off and I have to cycle the switch back to the headlight position and then back to parking lights to get them to work again..

Please help!

 

Anyone have any ideas?

 

a bad rheostat could cause this problem...

 

I replaced the rheostat since then.. still no luck

 

i'm starting to question whether or not this problem is related to my rear defrost situation.. My rear defrost won't stay on, if I hold the button it works, but as soon as I let go of the button it turns off.. But looking at my headlight problem, and the fact that my headlights stay on for aproximately 15 minutes, which is roughly how long the rear defrost is supposed to stay on, maybe the problem with the both of them is related?

I'm shooting in the dark here.. almost literally lol

 

Turns out the rear defrost was directly related to the headlight issue.. Did anyone know that both the headlight step up relay and the rear defrost relay have the exact same wire harness pattern? and that both relays are essentially interchangable? this was the cause of all my problems.. swapped the two back around and headlights started working properly, and rear defrost works like a charm!