Turn signals stop when brakes are applied

[Mr_Roboto]

This is on my 85 F350 in my signature. Both turn signals work fine, until you press on the brake pedal. Thinking maybe it was a load issue (tons of lights on this truck) I installed an electronic flasher unit. Same thing, no change.

It's been a while since I've dealt with these older trucks. Is this going to be a bad turn signal switch, a wiring problem or something else?

........................................................................................................................................

OK, I did a little more looking. When the turn signal is active, both rear lights are actually flashing. The front turn signal lights work properly.

I've checked the grounds at the rear lights, and also checked for burned out filaments that would short between the turn and brake circuits. Those things checked out OK.

 

[Mr_Roboto]

OK, I got it. Apparently the trailer connector wires got cut, and the PO connected the left and right turn signal wires together. Untwist one connection, and all is well again.

I was having nightmares of running new wires under the truck..

 

[Roland_Jenkins]

Glad we could help

 

[yARIC008]

Yeah.. i was gonna say, Mr Roboto with a problem he can't figure out!?? ;p

 

[Mr_Roboto]

, I can figure out other people's problems just fine.....

Here's my secret - when I was a kid my dad had a bunch of old (30's 40's) Motor's brand manuals he bought at swap meets. I read em all. Nobody knew anything about cars back then, so the books gave you all the theory (the why) along with the diagnostics.

I do have problems with the newer stuff. Motor's didn't cover computers in 1930!