Tailight Wiring '62 Overlander

[Deppdog]

I have a 1962 Overlander which I picked up a month or so ago. Upon inspection of the exterior lights - brake, turn, running etc. I have found a problem I can't solve. All of the exterior lighting works perfectly, except for when I turn on the right turn signal. When the right signal is activated, the left signal blinks as well - like hazard lights are on. No other lights are affected by this or any other variable of light operation. I have checked the truck plug end and it is OK. I have checked the plug end on the trailer and all is wired correctly with the truck end. I have checked the wiring at the access panel in front and it checks out OK - that's as far as I could get without tearing into panels. Any ideas? Anyone know where the wiring runs from the access panel?

Thanks in advance!

Deppdog