Tail lights and signals going whacko.

[tigerburns]

Finally resolution!!

Just an update to close out the thread...

So I checked my grounds and my connections with a circuit tester and found them to be good. I decided the problem was either in the rear wiring harness or the turn signal switch. As it turns out, it was both.

I got a new rear harness and turn signal switch from Eckler's (super fast delivery to my part of the country BTW). When I installed the rear harness, the lights were still blinking, however, they were now the same brightness. Previous, the driver side bulb had been much dimmer than the other side. I then installed the new turn signal switch (which also has a wiring harness attached). My original under-dash wiring was gathered together in a couple spots with zip ties. I noticed when I cut the zip ties that a dark blue wire (right turn signal) had a bare spot; which turns out, was creating the short. I put some wire insulation and electrical tape over the bare wire, hooked everything back up and Voila!! It all works as it should!

Whew!! Electrical gremlins are tough adversaries.
Plan is to eventually replace the complete wiring harness and fuse box for the truck to a more updated version. 50+ year old wiring can't be trusted.

Thanks for everyone's help on this board and thread.