Rewiring Trailer Lights

[Cris Askervold]

I changed out my trailer lights with LED's, first I ran the wires that came with the lights which only had a short ground that attached to the trailer. hooked it all up and only the brake lights worked. so I ran 2 full length ground wires as it was with the old trailer lights and now none of the lights are working. anyone, please HELP what am I doing wrong ?

anything drawings ect even in crayon would help.

thanks

[spartyon8]

Always...always...always check the ground. I always have issues with a ground somewhere. It is usually the ground wire at the plug. You shouldn't need two full length ground wires. Take some sandpaper and clean where all three grounds attach until they are shiney metal.

[Fishing Rhino]

Go back to step one.  The brake lights worked which means they had a ground.  Unless I'm mistaken, a tail light has three wires, one for the ground, one for the tail light, and the other for the brake/signal/hazard flasher lights.  That tells me the ground for the tail light assembly is okay.

 

Does your trailer have other marker lights along the sides.  If so they should go on the same circuit as the tail lights.

 

What type of plug do you have?  It should have at least four connectors, one ground, one for the running lights, one for the left brake/turn signal/hazard flasher, and one for the right brake/turn signal/hazard flasher.

 

They should be color coded, each being a different color.

 

You can buy a cheap automotive circuit tester at a hardware store.  All you need is the type that lights up when a circuit is on.  They can be found for about ten bucks.

 

Start with the plug on your vehicle.  Turn the lights on and the hazard flasher.  Find the ground, make a connection to the ground, then touch the other lead to each of the other contacts on the vehicle's plug.  You should get a steady light on one.  That will be for your running/tail lights.  You should find two that flash.  Those will be your brake/turn signal/ hazard light contacts.  To determine which is which, turn off your hazard flashers, then activate your turn signal, either left or right.  You should have one contact that causes the tester to flash.  That will be the lead to the side you activated with the turn signal.

 

Once you have determined that the plug on the vehicle is functioning properly, you can go to the trailer.  You now know which wire on the plug does what.  Make a drawing so you can identify each.  Then connect your trailer plug. 

 

Note which color wire is for the ground, the running lights, the left and the right turn signal/brake lights.

 

Make the proper connections and you should be in business.

 

Be sure to check the plug on the vehicle first to make sure it is okay.  Many vehicles have two dedicated circuits for the tail light operation.  One for the vehicle, and another for a trailer.  The lights may work fine on the vehicle, but have a blown fuse on the trailer circuit.  You may have created a short with those two long ground wires and blown a fuse on the trailer circuit.

[Team_Dougherty]

Brown wire running lights

yellow left brake and turn signal

green right brake and turn signal

White ground.

 

 

Lights with bulbs usually ground to the trailer frame with the mounting studs

Lights with LEDs will ground with the studs sometimes. other times they will have a white wire.

 

If your trailer is a bolt together you are better off running a white wire to the taillights connecting to the studs or white wire.

if your trailer is welded you can, most of the time, use the trailer as a ground.

 

 

 

[Cris Askervold]

the original wires with the LED's had 2 brown wires, one for each side, 1 green for the right and 1 yellow for the left. the lights had small white ground pigtails to screw to the trailer. that is when only the brake lights worked. and yes I do have 2 running lights on each side that connect to the brown wires. So I figured it had to be a ground issue. I that's why I went back to harbor freight bought the other trailer wire kit that came with 1 solid white that ran the length of all the other ones. I added a 2nd white to connect the other side and only connected the rear LED's not the side markers. and still nothing. where would the fuse be on the trailer circuit ? I'm dumbfounded I did connect the 2 full length grounds to the trailer connection and the trailer at a new area with new self tapping screw and that still didn't do it. I will check tomorrow the connection coming from my car maybe that's it ?????

[gramps50]

The biggest mistake people make is try and ground the trailer to the tow vehicle through the hitch. This does not work reliably. Always run the ground through the plug and like stated above make sure where the ground connects to the frame is clean and the connection is tight..

 

A bad ground can and will cause some strange things to happen.

[Fishing Rhino]

The fuse for the trailer circuit is usually found under the hood.  When you remove the cover to the fuse panel, there should be a schematic on the inside of the cover which tells you what each fuse is used for.  There may be two fuse panels on some vehicles.

 

It should also be in the owner's manual for your particular vehicle.  If you do not have one, search online. 

 

I found this one for my 2008 GMC Sierra

 

Fuses 3, 6, 10, and 24 are for the trailer connector.

 

 

[Team_Dougherty]

Sometimes, Like my GMC envoy, The trailer fuses are under the back seat.

[Cris Askervold]

well thank you everyone that replied, I was able to trace the problem back to the fuse at the battery, yeah that pesky little, sometimes overlooked thing called a fuse. feel stupid for not realizing it.  

[tcbass]

The fuse for the trailer circuit is usually found under the hood.  When you remove the cover to the fuse panel, there should be a schematic on the inside of the cover which tells you what each fuse is used for.  There may be two fuse panels on some vehicles.

 

It should also be in the owner's manual for your particular vehicle.  If you do not have one, search online. 

 

I found this one for my 2008 GMC Sierra

 

Fuses 3, 6, 10, and 24 are for the trailer connector.

 

 

 

 

 

I wonder which one your trailer running lights is?

 

 

 

My trailer lights all work but not when hooked up to my truck. When hooked up to my truck all of the trailer lights except the running lights work. I got a tester and it's bad from the truck. Hooked the trailer up to my friend's truck and everything ran great. I'll have to check the fuses.

[Fishing Rhino]

I wonder which one your trailer running lights is?

 

 

 

My trailer lights all work but not when hooked up to my truck. When hooked up to my truck all of the trailer lights except the running lights work. I got a tester and it's bad from the truck. Hooked the trailer up to my friend's truck and everything ran great. I'll have to check the fuses.

 Number 24 is the running lights on the schematic in my post.  Prk means parking lights.  Same as running lights.  TRLR PRK is Trailer parking lights.

[tcbass]

 Number 24 is the running lights on the schematic in my post.  Prk means parking lights.  Same as running lights.  TRLR PRK is Trailer parking lights.

 

 

 

 

Cool. Thanks. I'll check it out.

[Comfortably Numb]

Glad you figured it out.

 

As said, you cant always ground to the trailer