micro switch

Have you checked the micro switch in the head light rotating assembly?
If tis bad the head lights will only work with the park light switch on.

 

Sounds like a PO (Previous Owner) re-wired the headlights to power the main headlight relay from the parking light switch. Pretty common, when the micro-switches fail, and a PO doesn't take the trouble to fix them properly. Have a look at the wiring around the silver relay cannisters under the dash, and I suspect that you will see some non-OEM additions. Does the white dash indicator come on when the headlight buckets are partway up or down? If so, then the other micro-switches are still functional.

 

Destec Engineering Wiring Diagram

I bought a large laminated Opel GT wiring diagram from Destec Engineering on E-Bay, and hopefully that will help me figure out the headlight problem. I have tried to work off of the diagrams in the Opel manuals, and my old eyes can't handle that. This Destec one is great..all one piece, about 2 feet long, laminated, color coded wires, with tips on how to remedy some common GT wiring problems. I would reccommend every Opeler should have one. Gordy

 

This may be a dumb question, but was the key turned on? If not, your headlights won't work. Sorry, but I always look at the simple solutions first.