Passenger brake light not working

[Crusty69]

I have LED taillights. The running lights, turn signals, and driver side brake light works. What would be a likely issue causing only the drivers brake light to not work given that everything else is functioning.

[SRU1436]

I don’t have LED lights in my truck, but I’d start with the grounds. If I recall correctly, the housing is the ground. Not sure about how an LED grounds.

[Rust_never_sleeps]

Do the bulbs only go in one way? Diodes are typically unidirectional, so polarity matters

[RustyPile]

Originally Posted by Crusty69

I have LED taillights. The running lights, turn signals, and driver side brake light works. What would be a likely issue causing only the drivers brake light to not work given that everything else is functioning.

Ok, wait a minute.. I know your thread title says "Passenger brake light not working". But in second sentence you say the driver's side brake light works, and then in the last sentence you say it doesn't work.. Before I post a detailed description of the test steps, please clarify for me -- which brake light doesn't work...

[Crusty69]

Originally Posted by RustyPile

Ok, wait a minute.. I know your thread title says "Passenger brake light not working". But in second sentence you say the driver's side brake light works, and then in the last sentence you say it doesn't work.. Before I post a detailed description of the test steps, please clarify for me -- which brake light doesn't work...

Driver works, passenger doesn’t. Both turn signals work

[RustyPile]

Originally Posted by Crusty69

Driver works, passenger doesn’t. Both turn signals work

OK, that's better, here we go.. The turn signal switch performs a bit of magic in that it separates the brake light electrical current from the turn signal electrical current.. AND it separates all this current from the front turn signals..

The brake lights and turn signals share the same bulbs and wires from the turn signal switch.. So if the turn signals work properly, the fault is NOT grounds, bulbs, LEDs, nor wires and their associated connections.. Here's the procedure for testing:

Push the brake pedal to activate the brake lights. Locate the turn signal harness where it plugs into the main harness but do not disconnect it. Use a test light that has an incandescent bulb, not an led. Ground the test light lead and probe the dark green wire at the plug.. If you don't have voltage here, the turn signal switch is bad.

[PbFut]

If the front turn signal works correctly, then doesn't that indicate the switch is ok? Rusty, you know these trucks well. Is there some funky stuff with the switch and blinker that would allow one end to work and not the other? Do the easy stuff first. Swap bulbs to verify if its the bulb and or socket or not. Then very the socket is not corroded. Then verify if you have power at the socket. Then note color of wire. Go to firewall and unplug the connector on the 4 wire ribbon cable. Note the color of the wire matching the turn signal wire at the socket and test the pin for power on the firewall or jump 12v to the pin on the cable and see if the bulb lights.

[RustyPile]

Originally Posted by PbFut

If the front turn signal works correctly, then doesn't that indicate the switch is ok? Rusty, you know these trucks well. Is there some funky stuff with the switch and blinker that would allow one end to work and not the other? Do the easy stuff first. Swap bulbs to verify if its the bulb and or socket or not. Then very the socket is not corroded. Then verify if you have power at the socket. Then note color of wire. Go to firewall and unplug the connector on the 4 wire ribbon cable. Note the color of the wire matching the turn signal wire at the socket and test the pin for power on the firewall or jump 12v to the pin on the cable and see if the bulb lights.

Re-read my post.. The brake lights and rear turn signals share the same wires from the switch, the same bulbs, bulb sockets, and also the same ground paths.. Because of this "sharing", if the turn signals work as they should, then the problem with brake lights is NOT any of these items.. The problem is before the signal gets to the wires.. That's why I suggested testing at the plug.. I know the results of the test, there will be no voltage there.. I just wanted to "steer" the OP away from fiddling with all that other stuff and possibly creating another problem..

The front turn signals AND the dash turn indicators get their signal from the turn signal switch, but it is a totally different and independent section of the switch. To answer your question, No, that doesn't indicate the switch is functioning properly. It only indicates that section of the switch is functioning.

I realize wiring diagrams are very difficult for some people to read. But this is all laid out in the wiring diagram...

[Willshook]

Originally Posted by RustyPile

I just wanted to "steer" the OP away from fiddling with all that other stuff and possibly creating another problem..

I realize wiring diagrams are very difficult for some people to read. But this is all laid out in the wiring diagram...

Really good advice - I had some wonky light problems recently at it was that plug at the rear that was the whole problem. Someone had decided that was a good place to splice in trailer wiring and screwed it up big time.

Buying one of those big laminated color-coded wiring harness diagrams was a HUGE help for me - well worth the money.