Running and brake lights not working.

Alright guys. I'm a new member here and have a head scratcher. On the way home I was told I didn't have any tail lights (running and brake). I get home thinking fuse or something simple. All fuses under the hood have 12v going across. The fuses under the dash has zero. Even moved around some relays to see if it was that. Turn signals work, reverse lights work, hazards work also. No running lights, brake lights, or tag lights. I know they are all on the same power. I searched this place first and tried everything I read and no luck. I'm headed to ATL now so won't be back to the truck for 24 hours. Any advice would be greatly appreciated. Truck is 07 double cab short bed 6 cyl.

 

Firstly here is the circuit for the Tail Lights, and Tag Lights. You see that there is a Tail Relay that is energized only with the lights switch turned on. The Tail relay provides power to the Tail Fuse And when the Tail relay is closed everything gets power from the same source.

The Brake or Stop Lamps are sourced from a different fuse entirely. 10 Ampere Stop Fuse.

Did you check the fuses with a meter?
Was any electrical work prior to the lights not working?

 

You can see below where the circuits are different. The only common points are the alternator fuse some wiring and the battery.

 

No wiring work or anything done to the truck recently. I checked all fuses with a multimeter. The fuses under the hood are getting voltage on both posts. The one under the dash is zero both post. I'm going to take this diagram and start tracing it back. It has to be the relay if I'm understanding it correctly. I did switch around the horn and tail and horn relay and the horn worked. Maybe a connector on the bottom side of the fuse panel under the hood isn't making contact. Thanks for the diagram this will help.

 

I wish you the best of luck. These types of issues can be a pain in the ass to find.

 

Alright updates. I have stop lights. It's just all the running lights. My question is if the switch is bad the relay won't engage correct? I can turn my headlights on and off. So can a bad switch still turn on and off the headlights but not the running? I have 12.8 to every post at the relay except the bottom post. Electrical is not my thing.

 

I can jump a wire from the battery to the fuse box under the dash and the running lights work. Sorry for so many questions

 

Bump

 

You know your circuit from the fuse to the lights is good by the test you just did. Check the output of the combination switch while in park lamp position on the GREEN wire, if it's good, you have an or OPEN or relay that has failed between it and the fuse box you checked. Beware, the diagram shows the circuit going through the BCM before it goes anywhere else if you have the DRL option. The BCM could be at fault as well.

 

I'll try that thanks.

 

When in the parking lights position the meter is at ZERO. When in the off position it's 11v

 

OK, so the switch is pulling the circuit to ground when ON, (gives you the ZERO reading) and has ~12 volts when OFF, so the circuit to the switch is good. Try swapping the tail lamp relay out with another one if it's serviceable, sometimes these relays are integrated into the fuse/relay boxes on a PCB (printed circuit board)

 

Ok I'll do that now.

 

I moved around know working relay to diffespots on the BCM. There wasn't any change. I think my BCM has quit the team.

 

If you know someone or have access to a scan tool that can monitor PIDs, hook it up and watch the head lamp switch state when you turn the parking lamps ON. It should go from OFF to ON or NO to YES, if there is no change then I would suspect the BCM being at fault.

 

I'm looking into that now. Thanks for the help.