Brake light issue

[Nick joiner]

Let me start off by saying yes I used the search and google, but I'm not perfect and did a lot of skimming though so I may have missed it answered somewhere. If so I apologize.
86 c10 is what I'm working on.

Turn signals, tail lights, reverse lights all work correctly. Right side brake light works as well. Under the back testing the yellow wire, I have no juice with the brake only depressed. I do get juice off and on correctly with the left blinker on. That tells me the wire is good. Brake switch tests good also. What I'm down to is wondering if the turn signal switch could effect the brake circuit on just one side but leave the other side working fine. Any knowledge on this would sure help.

 

[diesel4me]

It can,but it is rare...

I recall a friends 1970 Ford F350 ramp truck having a dead brake lamp only,on one side,but not all the time...after getting pulled over several times we decided to scrap all the old tail lamps and bought new ones,and the right brake light still only worked when it felt like it...eventually I discovered if I pulled back on the directional switch lever with the brakes applied,both brake lamps lit up every time..if I didn't pull back on it,the right side only came on intermittently..

I would do a thorough inspection of all the tail light wiring from the fuse box back to the lamps--there is plenty of places they can be pinched,burned,or corroded,and also a 4 pronged plug near the rear wheels often corrodes (factory plug,so you can unplug the harness there,and take off the bed)...also if its had a trailer hitch installed by some former owner,its a good possibility it has corroded wires where they tapped in or cut the original harness..

Bad grounds are a common issue also...I had to put a bare wire on the tail lamp socket with a hose clamp,and run it to a frame bolt to get one of my trucks tail lamps to work properly,despite all the factory grounds looking good..