1984 Scottsdale, passenger rear turn signal and brake light

[Heliarc]

This is an odd one to me. Only the passenger rear turn signal and brake light are not working. All other lights are fine. I've eliminated the wiring outside of the cab as a possibility of the fault. I removed the section of the pug that deals with the lights and touched a hot wire to each connector. I can light them all up like this. The wiring from the main plug, sockets, and bulbs are good. The wire in question is dark green. On the inside it runs behind the fuse block and joins up with a big harness that goes up into the dash board. I have confirmed no power from the inside connector. Everything looks clean. The only possible hint I've got at this point, it's an original 305 gasoline engine truck and the fuel gauge has been swapped out to a diesel fuel gauge. The gauge is fine, it just tells me that someone has been in there. I've heard the turn signal switch is bad but I have trouble believing that since I can hear the relay going when I hit the switch. I would think the relay would do nothing and I'd have no turn signals at all at least on one side if the switch was bad. I'm going to pull the cluster tomorrow and look for any obvious problems. Has anyone run into this particular one with the rear passenger turn signal and brake light being non-functional? Again, everything from the firewall plug to the bulbs themselves are confirmed good. The problem is 100% in the cab.

 

[fast68chevy]

dark green is turn signal brake light filament wire. dark green is one side of truck and yellow is the other side of truck.
the one wire shares signaling and brake function, each side of truck.
the issue/problem most likely is the contact pin in socket for bulb back there, and it can be wire connection loose/bad/corroded. trace back on this wire with a test lamp bulb starting at socket, on that dark green wire with turn signal on and key switch run position and keep checking the wire, as you are moving forward along the rear lights wiring harness along the frame rail,, until the test lamp is blinking with the turn signal flasher, in the dark green wire, it sounds like bad wire connection in the rear lights wiring harness connector, or damage to the dark green wire, or bad worn signal switch contact for that bulb filament circuit(dark green wire)

maybe try fiddling with the signal switch as it is switched to signal that side of truck,, pull push on the signal switch stem handle see if it makes the test lamp or bulb start blinking or do anything at all... even if its only for a split second.. and if it does then this would tell you that you have a loose worn bad contact in the switch assy.
not much anyoine can do from a keyboard to help you on this one.. you have to test lamp probe and figure out how far back/where that you have signal voltage in the wire/circuit yourself. you should be able to pinpoint/trace out where the problem is with a simple probing-type circuit test lamp.

 

[Turbo4whl]

Check the turn signal switch.

 

[Heliarc]

The problem is definitely in the cab. I can run a 12V hotwire to the plug concerning the rear lights and light them all up including the brake/turn signal light in question. Can a failing turn signal switch work the front signal but no the rear? I can't wrap my head around that. The relay is working when I hit the switch, just not the rear passenger turn signal or brake. This is tough for me to wrap my head around. I'm not the electrical guy on any day. I'll have it opened up some more though. Can a bad turn signal switch mess with your brake lights?

 

[Matt69olds]

It’s entirely possible for the front bulbs to work, but not the rear. Check for power at the green wire at the turn signal switch, with the brake pedal pushed. Release the brake, turn on the ignition, try the turn signal while checking for power on the green wire. Still nothing? Push and pull the hazard switch a couple times and check again. Still nothing? Replace the turn signal switch.


There are a bunch of electrical contacts in the turn signal switch that each have to open/close for everything to work correctly. For what they do, they are pretty reliable.

 

[Turbo4whl]

The problem is definitely in the cab. I can run a 12V hotwire to the plug concerning the rear lights and light them all up including the brake/turn signal light in question. Can a failing turn signal switch work the front signal but no the rear? I can't wrap my head around that. The relay is working when I hit the switch, just not the rear passenger turn signal or brake. This is tough for me to wrap my head around. I'm not the electrical guy on any day. I'll have it opened up some more though. Can a bad turn signal switch mess with your brake lights?

To help your thought: Current from the brake pedal switch, when closed goes to the turn signal switch. Turn switch centered, this current feeds both rear lights.

When you move the signal switch for the right turn, the brake switch current can still feed the left turn, but now the right turn is being feed from the flasher current. So you have both feeds to the switch, but not to the right rear.

The turn switch could have one bad contact, or the wire connector is open, broken wire etc. The connector for the turn switch is low on the steering column.

 

[Grit dog]

If the turn signal switch has separate contacts for all 4 turn signals then it could be the switch still? Not familiar with the inner workings of the switch.
Considering a new switch is $18-30, if you’re relatively certain there’s not a short in the wiring going to the back somewhere, this is something I’d personally “throw parts” at and see if it solves the problem. Before tearing apart wire looms and whatever under the dash.
It may be a 36 year old original part that can/does wear out anyway.

 

[Turbo4whl]

If the turn signal switch has separate contacts for all 4 turn signals then it could be the switch still? Not familiar with the inner workings of the switch.
Considering a new switch is $18-30, if you’re relatively certain there’s not a short in the wiring going to the back somewhere, this is something I’d personally “throw parts” at and see if it solves the problem. Before tearing apart wire looms and whatever under the dash.
It may be a 36 year old original part that can/does wear out anyway.

OP's problem is most likely the turn switch, but he only has one more wire to check before removing the steering wheel and replacing the switch.

@Heliarc check the wire from the turn signal switch connector to the firewall connector. You know you are good from there to the light.

 

[Heliarc]

Dig it. I've been racking my brains. I get it now. I really get it and I can't thank you enough for the patience. I'm going out now to pull some stuff apart and see what's what. I will post a report.

 

[Heliarc]

Got it working. The wide connector on the steering column was partially disconnected...I think...I wiggled it and the light started working. I pinched it together and I felt a click. It's working. You guys rock! I never knew how the turn signals and brake lights interacted and I don't know if I'd have thought to check that connector. Thanks so much!!!

 

[AuroraGirl]

if you hadnt fixed it, i would suggest looking at the grounds or if the bulb is fully seated in a clean connector base. but beings you fixed it(yay) there is no need)

also a diesel fuel gauge should read "DIESEL FUEL ONLY" instead of "UNLEADED FUEL ONLY" and you would have a glowplug warning and if a tach was present i think it would have a smaller scale or have redline indicated differently

 

[Heliarc]

if you hadnt fixed it, i would suggest looking at the grounds or if the bulb is fully seated in a clean connector base. but beings you fixed it(yay) there is no need)

also a diesel fuel gauge should read "DIESEL FUEL ONLY" instead of "UNLEADED FUEL ONLY" and you would have a glowplug warning and if a tach was present i think it would have a smaller scale or have redline indicated differently

It has "Diesel fuel only" on the gauge. On the drivers front fender well there's something like a line setting ticket and it perfectly describes the paint job and other things as well as a gasoline engine. I only brought up the gauge to make note that someone was in there. Someone needed a fuel gauge and for whatever reason they put in a diesel gauge.

 

[AuroraGirl]

It has "Diesel fuel only" on the gauge. On the drivers front fender well there's something like a line setting ticket and it perfectly describes the paint job and other things as well as a gasoline engine. I only brought up the gauge to make note that someone was in there. Someone needed a fuel gauge and for whatever reason they put in a diesel gauge.

you could sell that its worth some dough. I dont need one but if you wanted a gas gauge i have a 78 and a 1980