Irritating electrical problem

[Maddog53]

Fairly new to me: kinda rough 1970 K-10 197K miles, Older Goodwrench crate sbc w/HEI, sm465, np205, ps, no a/c, wiring and electricals appear in pretty good condition.

The snag: Ignition "ON" and selecting a turn signal: The instrument panel's turn signal indicator lights go wonky when the headlights are also on.

The actual outside turn signal lights themselves work just fine regardless if the headlights are on or off. Likewise, the headlights work fine whether the turn signals are on or off. 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).

The malfunction seen is a dimmed pulsing of one or both (if high beams are selected) instrument panel turn signal indicator lights, or blinking of the wrong side (L or R) inst panel turn signal indicator light, and usually accompanied by a pulsing of the high beam indicator (if hi's are selected) in rhythm with the selected turn signal blinking.

Also rotating the headlight switch knob to dim the panel lights makes the turn signal indicator lights blink on the wrong (L or R) side...

Again, this is an instrument panel indicator light problem only; all the actual outside lights work perfectly all the time. I replaced the high beam selector switch, but no change in the malfunction was seen. I'm thinking this is a grounding problem as opposed to a "short." Sooooo..... if this IS a bad ground, where would a fella go looking for the problem....

Or, would experienced owners like you look for something completely different? Headlight switch? PC board??? I'm hoping someone's seen this before, and can guide me in the right direction, before I totally disassemble the whole truck as I'm prone to do...

Thanks a million in advance for your help friends! -Lee