[Dead Parrot]

Rule 1 for weird automotive electrical issues is verify that all grounds are good.
Rule 2 is check for corrosion.

After 30+ years, it is a rare turn signal or head light that doesn't have one or more corrosion issues. Especially for wires ran to ground screws. Most grounds involve bare metal and star washers that often react poorly to years of salt and moisture.

A lot of automotive circuits share wires and if a ground is bad, the current will back feed though a 2nd device to find a ground.