I have turn signals and brake lights on the trailer but no running lights. Everything points to a fuse but after pulling them all they seem good. Is there more than one fuse box on the truck

the bulbs are 2 filaments right? there has to be 2 wires unless there is a ground wire (3 wires) every trailer has to have a Running light, Left turn, right turn, and ground. th ebrake and turn signals work the same wires. you dont say what kind of truck you have, but some trucks have fuses for trailer lighting. put the 4 way flashers on and see whats wrong. if you have flashers you should have brake.

does the 3rd brake light in the back window work? check fuses if fuses are OK and the hazard lights work, then the turn signal switch may be bad. I dont know what your sons suburban (trailer?)has to do with your navigator?

Check the plug wiring again on the truck. You have a wire crossed , when you hit the lights and it only blows with the trailer, then there is a crossed wire on the truck. What seems to be happening is your sending power to the ground for the trailer. You can check the trailers ground with an ohm meter, then make sure your truck ground matches that pin. You may know this , but green rght turn, yellow is left turn, brown is parking lights, black is brake lights, and white is ground.

Have you checked the fuse box under the hood? There are seperate fuses for the truck lights and the trailer lights. If the fuses look good use a 12 volt test light to check for power on the turn signal pins when the brake is pushed. The brake lights and turn signals use the same wires to work. Power here would indicate the wiring and fuses on the truck is all good, meaning the trouble is on the trailer. Check the bulbs to be sure they are the correct ones, they should be dual element bulbs. Make sure you have a good ground on the trailer, usually the white wire in the 4 way plug is grounded to the trailer frame, do not depend on the trailer ball to be the ground, this is asking for trouble.

Trailer end; Red=Brake
Brown=Running lights
Yellow=Left
Green=Right
White=Ground
You will need a turn and brake signal box IF, you have different bulbs for brake and turn lamps. If the brake and turn bulbs are one(red)lens than no box will be required. Thanks, Dana

I have the exact same issue. I have also tested my trailer on other vehicles and it works fine. I even purchased a light up tester and found the problem at the harness. It seems like a bad ground to me but I can't seem to find one.

The trailer lights have a common brake/turn wire while the truck has seperate turn and brake lights. I think the problem lies with the device that marries the two for the trailer wiring but I don't know where to find it?

abad ground on that tail light unit could affect current load when turn and stop are used simultaneously. Although one side only is affected make sure of good grnd between trailer and tow vehicle. focust on the tail light unit in question. Replace the bulb. though rare, bulbs have been known to be the problem. If the bulb is breaking filiments ck the filiment orientation. filiments last longer in vertical orientation, where horizontal permits vibration to break the heated filiment when brake is applied.. good luck and let me know if This helped or not.

Hey Paul, it's most likely a wiring problem. There is one wire designated for just the running lights. What type of plug does the truck have? Probably 6 or 7 way (6 or 7 wire). You can check the plug-in at the truck with a multi-meter to see if there's power at that point. If there is, then the problem is somewhere from the trailer plug to the lights on the trailer. If you have a 7 way plug, the center plug is for aux. power (back up lights on what you pull, if equipped). One wire is power to the camper battery for a breakaway switch, one for left turn and stop, one for right turn and stop, a ground wire, one for running lights, and one for trailer brakes. To determine what wire does what, 1st with meter check volts of all wires w/ truck and trailer hooked up, truck running, power wire to battery for breakaway should show voltage if equipped w/ a trickle charge, brake wire will show low voltage, approx. 2 volts, apply brakes and should go up to approx. 12 volts, put on L turn signal, meter should go up and down, as power to blinker pulses on and off, do the same to determine which is the R turn signal (put foot on truck brakes will show voltage to brake lights AND brakes, continue w/ process of elimination to determine which is running lights, and exactly where power is not going.

It sounds like your have may have your brake light and running lights crossed on your wiring harness to the trailer. Good luck and hope this help's

check all trailer tow fuses in panel under hood.there is a fuse for trailer brake lights and a fuse for trailer signals.but if one signal is working it is probaly broken or corroded wires at the back of the trailer plug or corroded wires inside plug.