brake switch negated turn signals.

[jveenker]

ok, I need a little help.

68 F250 CS.

my turn sigs work fine when i'm not hitting the brakes, but, as soon as the brake switch (put the brakes on) is engaged, the turn signal doesn't blink. it just stay lit. doesn't matter which side. same for the emergency flashers. both sides flash when on but when i hit the brakes they stop blinking and just stay lit. Everything was working great for the last couple of years, any ides ?

[71highboy]

sounds like a problem in the steering column wiring

[Thunderfoot]

That is a problem with the Turn Signal Switch (TSS), this is where the brake light signal is disengaged so that the turn signals work. You will need to pull the steering wheel off and take a look at the TSS, you may be able to just replace the signal cam or it might need a whole new TSS.
It is normal for the emergency flasher to not work with the brakes applied, on our old trucks.

[jveenker]

thanks guys, will pull the column apart tom.

[jveenker]

So... an update.


I got a new Turn Signal Switch (TSS) from NPD and installed it in the truck. (that was a PITA). I ended up having to take the column shifter apart to get the wires fed down the column itself. When i put everything back together and preformed a functions check, I still have the same problem. . In Addition, the engine won't turn over cause It thinks its in a gear other than park. So tomorrow I'll be pulling the column apart again to make sure I got the linkage and shifter put back together right. However, I'm still stuck when it comes to my turn signal problems. any help as to where to start hunting around next? thanks for the advice in advance.

[Thunderfoot]

interesting... Have you changed any of the rear light bulbs recently? with the new switch does it still do it turning either way? One other question; has there been a trailer plug wired into the truck?

[jveenker]

negative on the rear light bulbs. Yes, it still signals a turn both ways without the brakes on, negative on the trailer plug.

[jveenker]

could this just be the brake light switch failing?

[Thunderfoot]

Negative on the Brake Switch it sends the signal to the TSS which is where it disconnects the brake signal during turn signal operation that is why we thought it was the TSS...
Got a test for you to try; without using the turn signal hit the brakes and see if the front turn signal light(s) come on... and also try unplugging the emergency flasher switch (not the flasher but the switch itself) and try the signals and brakes and see if they work correctly with it unplugged.

[fordman]

a failed brake light switch will only stop the brake lights from working. or turn them on full time.

[jveenker]

ok... interesting development.

with the emergency flasher switch unplugged and the left turn sig. on = both rear brake light flashing and front left turn on.
with emergency flasher switch unplugged and the right turn sig. on = both rear brake light flashing and front right turn sig. on.
with the emergency flasher switch plugged in but not turned on, when turning either left or right it operates the emergency flashers in both the front and rear.

i also tried hitting the brakes and the front lights did not come on.

[Thunderfoot]

Ah, now I think we're getting somewhere... From that you have a short in the wires to the back Brake/Turn signals with each other. Look under the truck and from the TSS connector back to the tail lights at the Green wire and Yellow/black striped wire, somewhere they are shorted/melted together.

[jveenker]

awesome, I'll get to that sometime today, thanks,

[jveenker]

an update:

I went through the entire wiring loom today looking for any shorts or melted wires. I fixed whatever looked questionable and took my time. I have two discoveries to report.

1) as i was tracing and following the yellow and green wires from the engine compartment and passed the tranny the loom went along the frame and between my aux. tank. This made checking the wiring impossible without removing the fuel tanks skid plate, so i opted to leave that as a last resort. At the other end of the tank I noticed that my primary loom continued back to the rear end of the truck, but, mid way down the aux. tank an additional wire loom was popping out and just hanging quitely from the skid plate. when i pulled it apart and inspected the wire colors there were green, yellow, red, white (ground), and what i thing was a black or brown. I surmised that this was a split from the main wires that at some time serviced the camper portion of the truck when it had a camper on it. (the truck is a CS). At some point in the trucks life a PO just hacked the wires off and didn't cap them off correctly.

2 after inspecting and fixing any thing that looked questionable the turn signals and brake lights now all work correctly when the emergency flasher switch is unplugged. I'm not sure what was the actual cause of my orignal problem but i suspect it had something to do with the extra wiring loom by the aux. tank.

Question: should the signals and brakes be operating correctly without the emergency flasher switch plugged in?

[Thunderfoot]

Question: should the signals and brakes be operating correctly without the emergency flasher switch plugged in?

Yep, that is correct and normal. It should work with it plugged in now too, I just want to eliminate that it wasn't shorted out internally causing the problem and it wasn't.

That sounds like the camper wiring you found and I bet that those exposed ends of the cut wires were making contact there, glad you got it working.