turn signal flash really slow ...

Bad grounds on the light sockets.

Clean all the ground wires everywhere. They tend to corrode just enough over 50 years that the electricity starts doing funny stuff.

Electricity follows the path of least resistance.

Corroded grounds > lots of resistance. The electricity is trying to find another way home... taking the slow route back to the battery.

Make sure you have at least 12.5 volts at your battery.

Have seen older batteries at 12 volts that have lost their push and fall on their face. Put in a new battery and things work amazingly well again.

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