Hopefully that will help out some. If you cant see something good, or want me to zoom in on a certain area, just let me know.

 

The wiring for the turn signals and brake lights goes through the turn signal switch in the steering column.
Replacing that harness is not easy and hopefully you don't have to do that.
I had a broken wire somewhere inside so the right front turn signal didn't work.
Then I had a broken steering collar, so I replaced it along with the harness and now all works properly.
There are multiple connectors from that harness to the wiring under the dash, and it is very easy to mis-connect them as the colors of the older wires has faded.
I have an automatic transmission, so if you have a manual, the columns will be a little different.

 

To be honest, that looks identical to the shop manual, but I sure appreciate the help!

 

Right, I'm hoping this is not the case. The fact that the fault seems to have developed during the course of the long winter's nap has me thinking corrosion somewhere, hopefully. Possibly vermin chewing on something. Maybe fresh, new wiring is more tender and tasty. It's got Soy! Bahstids.

 

I feel your pain. Be happy you don't have a 79 tilt column. Sometimes my left brake light works and sometimes it don't. I know it is a bad wire in that 40 year old switch. I just don't feel like spending $140 on a new made in USA switch.

 

Ok, messed around tonite with it for a little bit, no joy so need to do it smart. The connector circled is one right at the firewall. 3 wires, yellow green brown, should be able to isolate the fault at either foreward or backward from this point effectively splitting the truck in half.

The yellow wire at the connector should be hot to ground when either the brake is pressed or, when the driver side turn signal is switched, correct?

Only the driver side tailight is in this part of the diagram I cropped. I'm not getting a warm and fuzzy, overall because neither side brake light works. It looks to me they should work independent.

But the DVOM shows continuity at the pressure switch terminals (beeps) when pedal is depressed. If I short the wires, only the passenger side stop light illuminates. The front turn signals work OK, doesn't this (maybe) rule out the steering column wiring, or the switch? Argh.

Edit: OK, the test light probe at yellow wire terminal on the circled connector blinks, tells me the turn signal fault is somewhere Aft of that point. That's OK, I guess, I'll find it. At least it's not in the steering column.

My working theory now is the brake pressure switch itself died over the winter.

The wiring itself is OK on the passenger side all the way back, but stop light still won't work except when shorted and bypassed around the switch, and the turn signal & stop light shares same wire, so it most likely won't work in any case on the driver side, even after I repair the wire. That's my theory and I'm stickin' with it! Thanks for following along. Helpful hints, suggestions, snide remarks etc., much appreciated.

 

Just went through a similar situation with my 66 yesterday. After a lot of head scratching and cussing, turned out to be my brake light switch was stuck part way on. 7.4 volts never more or less. Switched sides with turn signal lever. New brake light switch cleared it up for me. Now brake lights are bright. All my rear wiring is redone for no apparent reason. lol

 

Yep, I've heard bad things about the brake switches on the market today. If I'm correct and this one is defective, it only lasted a couple years, and not too many miles, maybe 2-3k. The original 55 year old switch still works, or at least it did on removal, but I eventually replaced it on GP. After replacing the brake system, it was the only original piece left other than the pedal. Soon after though, I had genuine panic stop on the highway, and while I discovered the braking was excellent, the switch ever after was a little "lazier" than I'd like, it was slow to illuminate. I suppose I should switch to the mechanical type, but I'm stubborn that way.

 

Success! Cleaned up and Soldered up an old corroded splice and got the turn signal back, dropped the original brake switch back in and the stop lights work great. Still can't read a schematic but they sure help.

 

I made a couple of brackets and mounted a later plunger type switch om my '63...

 

Now, yer just showin' off! I like that, but that's above my skilz level.

 

I had to do something. I upgraded the master/booster and there was no port for the juice switch.