Ok, I have a weird issue going on. I have some ideas of where to look but would like everyone's thoughts.

1. Should the tail lights on a 69 superbee function when not in the bezel? i was under the impression that they had to be grounded inside the bezel to actually work.

2. The signals Right and Left will not function when the headlights or parking lights are on. Works fine when headlights are turned off. Also if signalling, when headlights are turned on signals stop working. Also if lever is placed on left or right signal and headlights on, as soon as headlights switch is turned to the off position they start working.

Thoughts?

Do you have a new wiring harness, and if so who made it?

Sounds like you have a very poor ground

Is this the after affect of any changes you made? If not, could be the turn signal switch is kaput.

My 69 GTX. Turn signals worked only in weird combinations, ditto rear lights and brake lights. Happened all of the sudden. I checked grounds, no impact. On a hunch changed out the turn signal switch, fixed all. Appears the switch was shorting out.

Ground issue. When only 2 wires go into taillight and front park/turn socket, it HAS to ground to body/ bumper.

Any tips on locating the grounding issue? Seems like with the headlight on/signal issue it may likely be in the turn signal signal switch.

I recall the taillights should not function unless grounded into the bezel. If they are unplugged the lights should go off. These stay on telling me the system is grounding them somewhere.

Where to start to look to improve the ground. Battery cable to AC compressor? block to frame?

The lights are plenty bright outside of the bezel:) appears to be grounded all the time somewhere in the system.

How many wires to each taillight socket? If 2 they ground through the housing. If 3 then they have a ground wire.
On my Roadrunner iirc there is a ground wire screwed to the latch support.

Same question for the front lights. Iirc the Roadrunner grounds through the housing.

with jumpers, connect the bulbs' metal housing(s) (both/all bulbs) to a known ground & see if this resolves it cuz that continuity is the bottom line for bulbs then if that is it you can go about reextablishing that continuity.

2 wires. it appears the taillight "hot" is what is performing as a ground to turn on the signals and brake lights on the rear.

The housing grounds to the body through the bolts. Clean the paint off the studs and nuts and try again.