[Lady72nRob71]

My guess is also that the rheostat on the light switch is defective.
They are easy to burn open if overloaded and the previous owners could have tried to hook something up to it that drew too much power...

Use a volt meter to trace the voltage back on the gray wire back to the switch. The switch is a bit of a PITA to change but I have done it. They are easy to find at most parts places.
If you do change it, be sure to change the most-likely-burned-out bulb behind the "Lights" wording above the switch. This 1445 bulb is in a small cylinder between the dash and the switch. Otterzone should have the bulb.

The light switch knob itself is a bit tricky to remove, from what I remember also. The manual did not describe the procedure right...
Holler if I can help more.