I hooked up my trailer lights everything works but my taillight

Round 7-Pin Wiring Diagram

• ? White Ground.
• • Brown Taillights.
• • Green Right turn / brakes.
• • Red Auxiliary power.
• • Yellow Left turn / brakes.
• • Black Reverse lights.
• • Blue Electric brakes.

Trailer Wiring Diagram and Installation Help - Towing 101

The 4-wire flat plugs usually have a white (ground), green (right brake/turn) yellow (left brake/turn) and brown (taillights - left and right). If your brake and turn lights work but the taillights don't, check the plugs (trailer and truck sides) for corrosion, and chek both the trailer and truck wiring harnesses for chafed insulation and bare conductors on the brown wires. Likewiae if the taillights work and the brake/turn lights don't, perform the same checks on those wires. And last but not least, be sure that the white wires (truck and trailer) are grounded well to the truck body and trailer frame.

suggest downloading the trailer pin standard for whatever number of pins your trailer plug has and tracing the wiring from the colors . The standard will tell you what color goes to what light and what pin number it should be on . Also 5 pin and 7 pin are different . You can plug a 5 pin into a 7 pin but the wiring is different .

Also check the trailer socket is grounded at the car body properly. As this can cause lots of weird symptoms.

Hello, if you only have taillights on the trailer and no side markers, check your bulbs first. The bright side is used for the Brakes and turn signals and the normal filament is used for the running lights.

If you use a test light you can find the pin on the connector which runs the Running lights. Sometimes the wiring harness will pick up the running lights off of the taillight in the bed of the truck. You would look for a wire going up into the taillight housing from the Trailer plug.

If you are the original owner of the truck there was a small package of Relays and wire ends that came in a plastic bag. It could be stored with the jack. This package had wire color information and instructions for Electric brakes. It also color-coded the Trailer plug-in socket as they use the extra pin holes for the Electric brakes. All the wires are discussed.

If an aftermarket unit was wired in the running light, the wires could be any color. The industry tried to put in a standard, but instructions still say if you don't have one color, its another. That is still vague.

If you don't have a 'plug' for the trailer taillights, then the trailer renter, like Uhaul, sells bulb adapters that hook into the tail brake and light lamps that can power the trailer taillights.

I remember, I had a 1980 Suburban that didn't have a 'compatible' plug, and that's the way we resolved the problem.

Good luck on this towing.

• Home
• Search
• Privacy Policy
• Contact Us
• Links

Trailer Wiring Diagrams 4 Way Systems

4 way flat molded connectors allow basic hookup for three lighting functions; right turn signal / stop light (green), left turn signal / stop light (yellow), taillight / license / side marker (brown) and a ground (white).

4 way tow vehicle side.
4 way trailer side.
5 Way Systems

Same as 4 way system listed above but adds a extra blue wire for brake signal or auxiliary power. Used on pop up camper trailers or utility / boat trailers.
5 way tow vehicle side.
5 way trailer side.
6 Way System, Rectangle Plug 3/4 inch by 1 inch 6 way rectangle connectors right turn signal (green), left turn signal (yellow), taillight (brown), ground (white). The red and blue wire can be used for brake control or auxiliary. Use on a small motorcycle trailer, snowmobile trailer or utility trailer. Can also be used as custom wiring on trailers with 3 light/wire systems. See "Tow Vehicle Taillight Wiring" below.
6 way tow vehicle side.
6 way trailer side.
6 Way Systems, Round Plug

Round 1 1/4" diameter metal connector allows 1 or 2 additional wiring and lighting functions such as back up lights, auxiliary 12v power or electric brakes. Note: The black (sometimes red) 12v and blue electric brakes wire may need to be reversed to suit the trailer. Check with a test light or VOM. Uses: horse trailer, travel trailers, landscaping trailer, car trailer, etc.

6 way tow vehicle side.
6 way trailer side.
7 Way Systems

Round 2" diameter connector allows additional pin for auxiliary 12 volt power or backup lights. Uses: heavy duty landscaping trailer, car trailer, boat trailers, horse trailer, travel trailer, construction trailer, etc. Check with a test light or VOM.

7 way RV flat blade tow vehicle side.
7 way RV flat blade trailer side.

you may have put wire in wrong terminal in plug

The trailer tow adapter parking lamps is fuse #10 in the cab fuse panel. There is also a trailer tow parking lamp relay that powers them, which could have a problem as well.
Start with the fuse, and maybe check both the 7 pin and the 4 pin for the parking lamps, could be a corroded pin on one of them causing the tester to not see the power on the pin.

taillights on what? Everything - needs to be grounded is the FIRST thing to remember. Try etrailers.com for parts or tech assistance or Google "Hoppy" trailer light kits.
Good luck

so, the trailer has no brake lights, or turn signals, just tail lights? Everything (all lights) on truck work ok? What do you have for trailer wiring hook up 4, 5, 6, or 7 way? There is no fuse, the lights all work off the tow vehicle lights, so if the tow vehicle lights all work properly, it's probably a wiring problem, such as bad grounds, loose connections, etc. Get a volt meter and check voltage at truck plug to see if power is getting that far. If truck plug in is ok, wiring problem is the trailer. Make sure all grounds are tight and rust free, that's a common problem.