Turn Signal Troubles

jeff1 said
Ground the headlight switch to the body at the steering column hold down bracket. The tail lights are looking for a ground path. Most headlight switches on these cars actually have a spade terminal on the switch housing. the switch normally grounds through the mounting in to the dash bezel. Over time this ground path becomes unable to support the current flow. Corrosion , too much paint , and lack of use. Remember it's the headlight switch housing that is to be grounded

This is not correct. Not one current path out of a headlight switch routes all the way back to and/or through the headlight switch. Current out to all lamps grounds at those bulbs and fixtures.
All replacement headlight switches will have a terminal for a ground wire which is required in some models ( one size fits all ). Where a mostly plastic inst' panel is mounted in a mostly plastic dash, they had to add a actual ground wire somewhere.