Park lights go off when high beams go on

[blkgmcv3500]

1987 V3500. When I turn on the headlights to the park light position, the headlights come on and no park light, when in the headlight position everything is on, turn on high beam, park lights go out, don't think the dash lights are working either

 

[Jgonick]

First I would check the bulkhead where it comes through the firewall. Make sure the 9-Brown wire(parking lights) is not switched with the 12-Tan wire (low beam headlights).

 

[Scott91370]

Ground wire loose.

But I did have an issue with lights as well and as Jgonick mentions the bulkhead - the bolt holding mine in place was loose causing me to lose power to front lighting.

If you do not have dash lights it's either ground, blown fuse (do you have taillights?) or the headlight switch is turned (not pushed) to the off position.