'72 turn signal flash on bumps

[BruthaMan]

Imagine you are sitting in a '72 truck, looking at your gauge bezel. Specifically the left turn signal indicator light.

One of the "features" I've had with my '72 since I bought it is, that every once in a blue moon when I hit a bump while driving, the left turn signal light will flash on momentarily.

All lights work normally, truck has been inspected and I drive it. Nothing really wrong, except the left side turn signal on the bezel will flash when I hit a bump. Only happens on the left signal light.

Plan to do some work on the truck this spring, so thought I'd see if anyone had suggestions on what to check, so I can add it to the work plan.