1964 d100 light switch defective?

[Mangra]

I have a 1964 d100, and when the lights are on, the turn signals don’t work. They both work fine with the lights off. When the lights are on, and I turn the signals either right or left, the rear tail lights weakly flash (both at the same time).
Is it time for a new light switch? It’s probably the original one.

Thanks
Robert

[MadMC63]

Check the ground straps between the bed and cab.

[PwrWgnDrvr]

That is a typical symptom for a bad ground somewhere in the circuit.