[Ol'Jim]

Thanks Ironic. Same bulbs have been in there for about 20 years. Replaced both flasher elements, (Turn Sig & 4-way Emerg), no change.
Bought a replacement turn signal switch from Ground Up (ss396.com), and installed it. Was an involved job, had to lower column, and cut off part of the flat plastic "conduit" that the harness passes through to get the old harness out, etc. - But not too bad.

Above problem is solved. Except - the dash turn indicators work perfectly with the headlights/park lamps off, but when headlights or park lights are on, then the turn sig lamps on the dash go opposite: R. Turn makes the left indicator flash, and vice-versa. The outside lights all function normally, just the dash indicators do this. Thinking maybe a bad ground somewhere in park lamp circuit?

Any ideas or advice will be appreciated, thanks!