I have a 76 highboy that we just finished the body work on. When I first got it the passenger side turn signal wasn’t working, nor were the hazard lights, and the brake lights would only come on when you were deep into the brake pedal. After cleaning the bulb sockets and replacing the bulbs I now have both turn signals, and the passenger hazard works, but not the driver. I found that with the left turn signal on and truck off, the drivers side hazard starts working. Also now the passenger brake light comes on as soon as you touch the pedal, but the drivers side still won’t come on until the pedal is pressed down pretty far. Also when the brake is pressed down and the truck is off if you get to the point where the drivers side brake light will come on and the left turn signal is on the front signal light and tail light both light up. Could this be the turn signal switch? Or did a previous owner mess up the wiring.

 

Probably the turn switch, everything goes through it. sometimes if you work the hazard button in and out a few times it fixes it if you're lucky.

 

Had similar issues, its the turn signal switch. I was abke to clean my contacts, with a brass wire brush, and everything works great. This so common.

 

You should have an adjustable depth brake switch on the side of the brake pedal, under the column. That might help with one problem?

 

I thought the same thing but the switch looks to be adjusted properly and is working now, because the passenger tail light comes on when the switch clicks. What I really don’t get is why when I get deeper into the pedal the other brake light works. I can’t see why that happens, but it’s a repeatable behavior. I ordered a turn signal switch, but will try to clean the contact points as suggested above first. Looks to be a strait forward but annoying replacement process.

 

You have a combination problem. The hazard/turn signal switch is the only place that can tie a front turn to a brake lamp. There is no 2 step in the brake switch unless you have cruise control and then you have 2 brake switches. Also sounds like a bad ground at a socket. When your left front signal illuminates is it actually the turn element or the parking element? Signals only work with ignition or accessory feed. Brake and hazard lamps are full time powered. The bulb sockets of the era are a 2 part affair, the bulb ground wire is actually 2 parts and can break contact from corrosion internally. What do your instrument turn indicators do when this is going on? Is the problem repeatable with the headlamps on? It almost always come down to a bad ground somewhere. Battery ground to block, cab grounded to block, box grounded to? Sorry to ramble on, but electrical back feed can be hard to trace.

 

As I recall, the steady 12vdc feed for the brake lights get interrupted by the signal switch to allow signaling with the same bulb filament via flasher controled 12vdc while brakes are applied..

 

Grounds are provided by body sheet metal, 2 flashers are required because 1 is full time power (4 way) and other is ignition powered. Whatever the problem is, if a dash bulb turn indicator lights up dim or full it will be a ground. Side marker lamps can also do an alternating flash like gm did in the day with a bad ground. Sorting out the dentsides turn and brake lamps is like the X files. Follow the trail. Factory shop manuals have diagnostics, flow charts actually easy to follow. Previous owners modifications can be a nightmare to follow.

 

So thanks for all of the help everyone. I replaced the turn signal switch and that fixed most of the issues. I have turn signals and brake lights now. However now when I step on the brake beyond halfway the turn signal stops only on the left side, I also replaced the brake switch. Everything seems to work when the brake lights first come on, brake lights come on turn signal cancels the brake light and flashes, but when I get deep in the pedal the signal stops flashing and I just have brake lights. No idea why when I get farther into the pedal it changes anything the brake light switch is active in the first little movement.

 

Reads like somehow the steady on brake liight feed that got interupted in the signal swith gets re-fed on left side with harder braking? Were there any "issues" with the signal switch? Any sketchy wire insulation?

 

No sketchy wiring at the column that I noticed, but I’ll look further. I got a new pigtail for the brake lights because the ground strap was a little rusty. The only sketchy thing I have found is the previous owner had installed a 7 pin and 2 4 pin trailer connections maybe something is wrong there.

 

that's actually a problem more often than it should be. No consistent reason that I remember hearing about. Just that things went wonky when trailer wiring was installed.
maybe a higher load on each circuit due to something wrong with the connections? Not sure...

Paul

 

it does have a trailer brake on it that must have been on the truck since new. It’s tied in at the master cylinder and works off of brake fluid pressure. Maybe disconnecting that would help.

 

Now you are onto something,

I once had just such a trailer brake control, was made by Kelsey-Hays, green metal housing under the dash, was operated by a steel hydraulic brake line from a tee on the side of the master cylinder, line went through the firewall. It also had a lever with **** on it that you could turn to adjust braking rate of the trailer with pedal pressure, or move it right-laft by hand to apply just the trailer brakes. It had a rheostat inside the box to fine tune trailer brake action with pedal pressure, and a big block under the dash with a long coil spring seciured to "posts" to adjust base line brake reaction as I recall, it also had a brake wire wire so that if you manually aplied the trailer brakes to maybe straighten the trailer, it would operate brake lights on the trailer.

I'll almost bet $ that in wiring those plugs, the trailer brake control brake light wire was tied into a truck brake light wire and once you mash hard enough to activate the controler brake light wire, that brake light is getting lit from there. If the controler didn't have that brake light wire, there would be no brake light showing when you manually work the brake lever on the box to straighten a trailer sway as the truck's brake pedal was not being depressed..

Mine started leaking brake fluid from the short slave cylinder in the controler so I removed the tee and brake tube feeding it, but kept the controler to use the manual lever while I had that camper. It's all gone now, except that block with the coil spring adjustable resistor, but it's disconnected.

Earlier I wrote that maybe it was brake light grounding that got interupted by the turn signal switch to allow signals,, but I then thought more on it .... it's the pos. 12vdc brake light feed that get's interupted by the turn signal.

I goofed earlier, but have corrected those two posts .... it's been a long time since I had given thought to that deal. I know better but just forgot ... those lights all ground at the body, no interuption. I think was maybe something else, maybe an old motorcycle even, that had the brake light grounds interupted for signals ... certainly was no "Dent" side Ford.

 

Thats the exact trailer brake controller I have. I ended up just cutting and taping the stop light wire from the trailer brake for now. I need to disco and drain that brake line eventually, but it’s not leaking and looks solid so nothing urgent there. It looked to be connected all the way at the back at the 7 pin connector. All tail lights are working and the signal switch is no longer being canceled. So I guess the turn signal switch was bad and the trailer brake was shorted somewhere causing the issues I had. Thanks all for the help!!