[Guest]

I have a '66 hardtop six cylinder chassis with a c code 289 warmed up with a autolite 1958 670 cfm, wiend dual plane dome, headers, 2 1/2 inch duals, electric fuel pump, and a couple of other upgrades.

When I signal left no problem. When I signal right both rear tail lights flash. Also, when I apply the brakes the right indicator light on the dash lights up as does the front right signal light.
So far I have replaced the signal light switch assembly,all bulbs, flasher unit, checked most of the wires for shorts and grounds. No luck, still the same problem. Any suggestions would be greatly appreciated.

 

[My427stang]

I am sure its a bad ground to that side. Check those very closely and make sure its a good ground. Very common on pickups when the beds get rusty, and it behaves exactly the same

 

[Guest]

You might want to check/replace the light switch also. Check out
http://www.hammar.dyndns.org/wiring/66exter1.jpg as a lot goes
back thru it. hope this helps.