Gremlin Hunt (67 Convertible Rear Lights)

[TCheo]

'67 Deville Convertible

I'm getting closer to roadworthiness but man this car is giving me a run for my money.

I'm chasing an issue with the rear lights. So tail lights and turn signals work all the time. The right brake light only works when the left turn signal is on.  The left brake light only works when the headlights are on. Also, the turn signals blink too slow when headlights are off.

Bulbs and sockets are good, of course. I have a new headlight switch available through work, the turn signal switch I'll have to buy online, brake light switch is new.

Has anyone had issues like this? Where should I start before I start throwing parts at it

[TJ Hopland]

Thought you were looking for an AMC car.....

Grounds are by far the most common issue with the lighting.    Another issue that can come up with these era cars is getting the wrong bulbs in some of the sockets.   There are a couple different dual filament lamps and singles will often fit in the same sockets so that could cause things to interact.   

The turn signal switch is also possible because it does a lot of routing so if its having issues there could be strange things happening but like I said grounds are much more common to be the problem. 

[TCheo]

Hmmm. Perhaps I should have thought through that subject line more! Nope, I'm happy with my Cadillac, there's just little AMC cars driving through my electrical system. Thank you for the advice. I'll double check grounds. The bulbs are definitely dual filament, correct bulb numbers. My problem is probably at the switch because all of the filaments light up at various times under various conditions which would mean proper contact at the socket, but the routing of the power distribution is only working sometimes

[fishnjim]

If it's one of the ones that has the "bulb out" feature, the turn signal light on the dash stays on, then the flasher has to be the right "type".   There's two kinds, a thermal and a electronic.   The routing is done on the dash circuit board and those can go bad.  (Need to pull the dash.)
If you get to the point of no hair from pulling it out, then call an auto electrician.   More familiar and better diagnostic tools.
DIY, it takes a while to get all the bugs out, and some you may have to live with.   Even when things appears right they may not work.   Probably needs a new harness if it's the original.   
Easy to cross wires also.   Some of the connectors are the same, L & R, and can go into either harness.   When I put my rebuilt motor back, I had the radiator support out, so all the front wires were disconnected and putting it back in, I inadvertently crossed the connectors at the support.   When I fired it up, the headlights would blink with the turn signal.   So patience.   Hurry is fraught with errors.   Check it, double check it, and check it again, is my motto.   Military based procedure to reduce possibility of error.