Irritating electrical problem

[MikeB]

Originally Posted by Maddog53

ONLY the instrument panel's indicator lights (including the high beam indicator light) malfunction when the headlights are "ON," AND the turn signal switch is activated to either side (L or R).

A couple weeks ago I saw very similar symptoms on a hot rod Ford with aftermarket instrument panel and a wiring harness built by the previous owner. It only happened when the parking lights or headlights were on.

Turns out the ground side of the turn signal and high beam indicator lamps were all tied together, but weren't grounded to the panel itself, the body, or the frame. I never did figure out how they lit at all, but grounding the bulbs to the dash fixed the problem.

So, check those grounds! On my 69, I think there is a single ground trace that runs around the printed circuit. Make sure that trace is grounded well. There should be very little resistance (0.5 ohms or less) between that point and the battery negative terminal.