Headlights off: When I put the right turn signal on, both signals flash, like hazards. Dash does the same thing. When I put the left signal on, nothing.

Headlights on: Right turn signal flashes, but only half as often as it should.

1) Where is the flasher relay located? (I can hear it, but can't see it)

2) Any other ideas?

Thanks.

Sounds like you lost a ground to the (perhaps) front turn signal lamps in the bumper. There is no ground wire and these lamps rely on a good frame ground. Also might be missing the small ground wire from battery (-) to the right inside fender. This wire gives the sheetmetal a good ground.
Try running a test wire from battery (-) directly to the front turn signal lights. Touch the signal bulb base right where it meets the glass. See if this changes the flashing behavior.

The fender ground is definitely good. I just cleaned it up while I was troubleshooting my horn.

I didn't know that about the front lamps. They are not grounded because the front bumper is off; just hanging there right now. They don't come on with the markers or turn signals. Thanks for the info.

I'm pretty sure the flasher has at least something to do with it, only because the rights flash and the lefts don't. I just can't seem to find it. I know I must be looking right at it, because I can hear it. Anyone know exactly where it is on a '66?

Happy Thanksgiving.