When the headlights are off, the blinkers and brake lights appear to function fine. Once the headlights are on, the brake lights are always full bright. Also when the head lights are on and the left signal is engaged it stays lit and does not blink, inside and out. Right side blinker seems fine blinks fine when the headlights are on.

Another odd problem is that when you are making a and turn the signal switch on – while you are making the turn, still in turn, the turn signal switch snaps back by itself. This happens on either side almost always

The turn signal switch has been replaced prior to my purchase of the truck.

As of the moment I have tried to do any diagnosing, however I do have a full turn signal switch come in from Dennis Carpenter.

Any other suggestions

 

Hey there. I’m always sorry to hear about these oddball electrical issues. But it sure sounds like a bad ground in one of the tail lights to me.
I’m not sure if your your truck has separate ground wires, or just relies on the connection between the metal tail lamp housing and the body.
Either way though, the grounds can fail or weaken over time. Causing some of these issues.

have you noticed whether or not your bright tail lights get dim when you hit the brakes? Or do they stay bright?
on some trucks, or at least the Broncos that use the same tail lights, there is a separate ground wire but that is only for the back up lamps. In early 66 they did not have back up lamps and they were added later that year and a separate ground was utilized.
If the housings are new they might be wired backwards too.
This is a problem that’s been going on for 10 years or more where the suppliers are getting their product from China wired backwards and don’t care enough to change them. So when it comes to those housings we literally have to swap the wires around on every one we get before we can sell it to a customer.
if you have new housings, check the wire orientation.

anyway, at least check the ground connection to the body. And in the case of an old truck where the connection between the bed and the frame might be questionable with Rust and paint and gunk, run a separate ground wire between one of the bed struts underneath and a bit of the vehicle frame.
Then also make sure there’s a good ground between the battery, or other well grounded component in the engine compartment and the frame up front.
Doesn’t have to be a big ground either. Since it’s only running tail lights and maybe one or two other things that are light amp draw, a 10 gauge wire is all that’s needed at the most.
You can usually get away with 14, but when it comes to grounds, overkill is just enough!

good luck

 

Thank you for the reply, your thoughts are most appreciated, I will in fact check all the grounds wires this weekend and see if that changes anything, and on the same thought I also may try and grounding the tail light bulb housing additionally with a jumper wire and see if that makes a difference. Take care and I'll post an update soon