Ok here goes my problem my 90 EF sedan light or combination switch isn't working well at all I turn on the parking lights every thing is fine with the car running but once I turn my head lights on the tach goes to zero the temp gauge goes to hot and the car is not even warm yet also I tried turning on the hazard lights while just the parking lights are on its fine but once I turn the head lights on the hazard lights stop blinking also when the parking lights are on my turn signal lights on the cluster light up dim and seat belt light. I've checked all grounds and my car has no radio. So if anyone has any ideas what this could be please share your thoughts.

 

Well obviously when you switch the headlights on they are triggering something so why dont you test each wire on the headlight switch to see which one is supplying power or switching on and off when you turn the switch on and off and then trace those wires further down the line to see if they have been modified.The helms manual will also help with wire colors and circuit diagrams.

 

Alright ill give that a try siblues thanks.

 

You have a grounding problem, when differant circuits "interfear/effect" each other it is almost always a grounding problem, check your head light grounds and your cluster grounds. 94