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Hey all, just noticed last night on the way back from the track, I had no trailer brake lights. Not sure how or when this happened, I rarely drive at night.
what I tested today, all fuses are good, turn signals, hazards, marker lights, all work on the truck, which means all bulbs are good. Tested at the brake switch, and both sides of the switch get 12v. Disconnected the switch from the pedal and manipulated it, still no lights. I feel like one side of that switch should be 0v and pressing the brake connects the circuit turning on the light, so I THINK it’s a ground issue....
Disconnected fuse #5 and killed circuit to both sides of the switch. Leads me to believe something is backfeeding voltage into the circuit. I’m wondering now if I completely disconnect the electronic brake controller, I’ll get the brake light back.
Interesting note is that the electric brakes on the trailer work (which are fed off the brake light circuit) but still no brake lights....
The bottom of fuse 5 gets constant voltage and the top side is grounded (red wire white stripe) connecting the fuse somehow sends voltage through both sides, so I’m suspect of the red wire white strip back feeding the circuit and not grounded properly.
1. Is this solely an issue of the brake lights on the Trailer not working? Or no brake lights on the truck either? You mention all the others working on the truck but specifically point the issue out as 'trailer brake lights' so just want to see if we need to focus on the truck or trailer.
2. Do you have the factory trailer wiring?
3. When testing voltage at the brake pedal switch is the key off or in run?
1. Is this solely an issue of the brake lights on the Trailer not working? Or no brake lights on the truck either? You mention all the others working on the truck but specifically point the issue out as 'trailer brake lights' so just want to see if we need to focus on the truck or trailer.
2. Do you have the factory trailer wiring?
3. When testing voltage at the brake pedal switch is the key off or in run?
tested with trailer, and without, just to rule out the trailer was the issue, and/or providing a ground that the truck wasn’t. The truck itself does not have brake lights.
It does have the factory trailer wiring, with an aftermarket brake controller and 7-way plug.
If I disconnect fuse #1, which is stop/hazards, the switch seems to work like normal, power to one side, not to the other, push pedal and gets power to other side, but still no brake lights.
the flasher bulb relay was swapped out to the turn signal side and it works as it should.
This plunger was also on the pedal, seems to be a vacuum switch of some sort, it wasn’t touching the pedal and not sure what it does, when you push the pedal it would seem to disconnect. Regardless, it was not contacting the brake pedal.
*edit, this is the cruise control vacuum servo switch, disregard, it’s not hooked up any more. Thought it was suspect but not anymore....
The bottom of fuse 5 gets constant voltage and the top side is grounded (red wire white stripe) connecting the fuse somehow sends voltage through both sides, so I’m suspect of the red wire white strip back feeding the circuit and not grounded properly.
How do you know the other side of the fuse is grounded? Are you taking the fuse out and putting the meter on ohms and reading the fuse terminal? That will tell you nothing. This circuit is obviously not grounded or the fuse would blow when you put it in.
Not sure what year you are working on, but all these years are mostly wired the same. The diagram below shows the brake light circuit. The big grey box is the turnsignal switch.
Hook everything back up and as original. Make sure you are back where you were, and everything works except the brake lights.
Then take your meter (a testlight would work better for this) and hook one side to ground, and poke the lightgreen wire. It should read like it did over at the brakelight switch. Make sure the turnsignal lever is in the center, and then poke the lightgreen/orange wire. Press the brake. You should get 12v on that wire. Then move the meter over to the orange/lightblue wire. Poke that wire and then press the brake pedal. You should get voltage on that wire. If you don't get voltage on either wire, there is something wrong with the turnsignal switch. You could try pressing the brake and then fiddle with the switch and see if they try to come on.
pulled the steering wheel and played around with the switch, realized nothing was working....
the factory plug had broke off the locking tab and the plug had disconnected, plugged it back in tight and everything works. I guess I’ll see if I can zip tie the connectors together.
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