89 mustang 5.0 crazy headlight/dash gauge problem

89foxbodyHO said:

Is there a seperate ground for the high beams somewhere? Or any other grounds that have to do with the headlight/blinker assembly that i dont know about?

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I looked at the wiring diagram I have and there is one ground per side for all the front lights except the fog lights.

Anyone know how this problem was solved? I am having the same issue with the temp, tach, etc. going crazy when I turn on my headlights. I've checked the two grounds for the headlights, the engine to firewall, battery to fender and they all look good. I read elsewhere that someone thought it could have something to do with a bad instrument voltage regulator? Could that be it?