This is driving me crazy no right brake light but when I turn on left turn signal right brake light works. This all started after I install a new turn signal switch in my 79 Bronco, old switch would not stay select and had to held down to get blinkers to work. After I install new turn signal switch I had no right brake light just left. This is how I think turn signal switch works, they're a 12-volt source from brake switch and they're a 12-volt blinker source for left or right turn. Both brake and blinker power are routed through electrical contacts in turn signal switch, which share the same tail light wires going back to tail lights and using same filament in bulb, correct me if wrong. With turn signal in off position and stepping on the brakes I only get left brake light no right. Both left & right turn signal work just fine, now when I select left turn the left tail light blink like it should and the right brake light comes on when applying brake same goes for right turn with left brake light working when applying brake. With battery disconnected I ohm out turn signal switch could not get reading on bolt tail light wires from brake switch just left side with turn signal in off position. Ohm out wire from flasher to left & right tail light turn signal both works as they should and when using turn signal brake light work as they should. Thinking turn signal switch is defected so got a free replacement switch and install same thing no right brake light when turn signal in off position, I need help! Where am I going wrong?

 

Okay new day sun is shining, took the first new turn signal switch that I install that didn't work no right brake. On the workbench pull the single screw that holds down rocker assemble in turn signal switch made a drawing of electrical contacts & wires showing mechanical movement of contacts function. Doing this show how simple the device was switching from brake switch to turn signal using same set of wires running down to tail lights and using same filament in bulb. With nothing to lose bent up contact wire spring that kind of looks like cat whiskers about the thickness of a standard paper clip to give more tension riding on contacts there two of them one for brake switch one for turn signal flasher. Put back together and holy crap it works, hope when bending didn't weaken spring tension. I will now do this to the second turn signal switch that still install in bronco. I will only have to remove steering wheel which by now can do in five minute to make adjustment. No doubt this stuff is coming from China pure junk will post result.

 

Good news got both brake lights to come on now, tweak both cat like whiskers that make contact with electrical contacts in turn signal switch. Also had to back off of two screws that hold turn signal switch assembly to steering column as turn signal arm seem very stiff and fail to return to center position until I loosen 2 screws just shy of snug. There a very small leaf spring that center rocker assembly when turn signal is in off position. Thinking this may have been the main cause in the first place but the first fail switch I repair was tested on bench free from any distortion from tighten screw to steering column. Good grief we shouldn't have to repair new parts my original turn signal switch is made with unknown yellow plastic. New switch looks made of nylon and not as stiff part # SM61F Brand Shee-Mar. There is a metal base plate that the plastic part sits on with 2 screw holes that screw to steering column. Looking at original Ford part plastic part lays very flat on metal base where new switch they're a gap between metal base and plastic part. I'll keep my fingers cross on all long the switch works maybe start looking for replacement now LOL

 

an old refrain.... clean up your grounds, too. It's amazing how many weird electrical gremlins can be cured by that.

 

And the older the wiring gets, they seem to breed more gremlins. Had kind of the same issue with an '02 150. Every single component got a bath.