Hi:
This is a tricky one to repair. Somewhere in the electrical, when you pull the headlight switch on, rather than power going to the park light, it's backfeeding to the interior signal light. This is usually caused by a ground problem. The only way to find it is to start at the tail light and work forward. Also, before you go crazy with the wiring, try replacing the light socket for the park and signal lights. The socket itself may be bad.
Let me know what you find.
Joe
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Saturday, December 13th, 2008 AT 2:16 PM