U-Haul Tail Light Wiring Diagram

[Craig D. Thompson]

I am quite baffled with the tail lights. I am preparing for a 6 day trip starting August 11. I decided to install some temporary tail lights because the original ones are very dim. I have been told a few times by drivers that were following me that they were not working. They do, or did work, but just very dimly. (This winter I will be performing a frame-off restoration, including new wiring & lights.)

Today I pulled off the lenses to see if I could temporarily wire some auxiliary tail lights.

The plugs connecting the wires from the light housing to the trailer wires are not tight so most of the connections came un-connected when I pulled the housing from the trailer. It should be a simple matter of figuring out which wires to connect one would think. Two bulbs, two wires to each bulb, running lights and turn signals.

I can get the right side to work: running light lower (red), turn signal upper (amber) + lower (red) blinking.

On the left side only the turn signal works.

This is really frustrating because the lights were working before I pulled out the housings.

Several questions come to mind. I am hoping some of you U-Haul owners might be able to answer them.

Does anyone have a wiring diagram for the U-Haul CT13?

When operating the turn signal, does the upper amber and lower red light both blink?

What is a typical voltage that powers a brake or turn signal bulb? I am measuring less than 1 volt.

I did some searching on the forum and found a few good threads about the CT13 tail lights but they did not answer all of my questions.

As always, any assistance is most appreciated.

Craig T.

[mary and bob]

The upper bulb socket only uses one of the two wires, turn light only. They did use a two wire socket there but only for standardization purposes. So you'll have a ground wire to each socket, or maybe one ground that is common to both, I don't recall. Lower socket, the red part of lens, uses both wires that come out of the socket, one is tail, other is stop. IF, big if here, your trailer has the original wiring, there would be two wire cords that come out of the tongue, one on each side. one cord for left lights, one for right lights. The marker lights are not all on one cord, some on each. I don't recall the original color code. What I found with our trailer was those original cords were dry rotted and cracked right down to bare wire in spots under the trailer. I pulled all the original wiring out except what was in the walls to the markers and rewired using modern color coded trailer wire. They also used those scotch lock connectors in many places inside. So between the scotch locks and possible cracked wire you have potential places for broken or corroded wires. When I rewired I only used the red part of the lens for tail / turn / stop. Since you have the tail lights apart, replace the bulbs, polish the lenses. There has been some discussion on the Uhaul Facebook group about using aluminum foil or paint to improve the reflective quality of the bulb housing.

[Bob Miller]

I would almost bet that you can save both time and grief if you get about 40' of quality Flat-4 cable and run new wires from your tongue back to each light, joining them together at the front for your TV's connector.

As wires and connections age, all kinds of repeat and mysterious problems arise. There are standard color codes for trailer lights and you will finish with a spare wire on each side. The last flat-4 cable I bought was not only color coded, each colors function was stamped on the cable every 12"... Easy-Peasy

[mary and bob]

I used the 4 wire flat, ran it back to the right tail light following the original routing, then across the rear inside to the left tail light. On my Uhaul the marker wires dropped down out of the wall in the closet area and behind the sink. I have a rear rack, so put extra lights on it for improved visibility. When not using the rack there is a light bar that goes in it's place, so I have an extra set of lights at all times. Next project, high mount stop / turn lights

[Craig D. Thompson]

Thanks for all the input folks, most helpful.

It is looking like the primary problem is with my TV. The voltage for the running lights in the electric socket on the car is about 0.4v. Presumably this should be 12v?

I measured this last night and did not have time to begin locating the cause.

The trailer tail lights still need to be re-hooked up but it will help greatly if the car is delivering the correct voltage. The wire colors are different on the light side and the trailer side (looks like original wiring), so if anyone has a wiring diagram it might help, though it should be simple to determine (once the car side is fixed).

Will keep you appraised of the progress.

[mary and bob]

If you do not belong to the Uhaul Facebook group, you need to join. Tom just a couple days ago posted wiring diagrams. He did it a couple ways, using just the red part of the lens, or using a converter to enable use of the amber for turn lights. It's probably in the files section there, along with lots of good information specific to Uhaul campers

[Bob Miller]

Originally Posted by Craig D. Thompson

Thanks for all the input folks, most helpful.

It is looking like the primary problem is with my TV. The voltage for the running lights in the electric socket on the car is about 0.4v. Presumably this should be 12v?

I measured this last night and did not have time to begin locating the cause.

The trailer tail lights still need to be re-hooked up but it will help greatly if the car is delivering the correct voltage. The wire colors are different on the light side and the trailer side (looks like original wiring), so if anyone has a wiring diagram it might help, though it should be simple to determine (once the car side is fixed).

Will keep you appraised of the progress.

I would inquire about how your TV's tail/turn light feed is hooked up. Some vehicles use "Ground Seeking" circuits for lighting, meaning that 12 volts always goes to the light and it is grounded through the on-board computer, meaning you can't just tap into the existing lines. But there are adapters. I suggest you check with a known trailer hitch place or Uhaul to find out how they are supposed to be connected before any damage is done to your system.

[Craig D. Thompson]

On Saturday I began "fixing" the tail lights. I have a trip coming up in 10 days so they had to be fixed this weekend, next weekend at the absolute latest.

By early afternoon I had the running lights, turn signals and brake lights working...but not all at the same time! Turn signals would not work when running lights were on, etc, etc.

I realized that Bob Miller is correct. Much less grief to put in new wires than try to debug the old. The local NAPA auto parts store had two rolls of flat four wire, 25' each. I bought both in case I needed them but one 25' length is just about perfect. Ran the wires back along the tong, to the right side, up through the floor under the closet next to the original wire, back to the right tail light, across the back to the left tail light. It really was not difficult once I resigned myself that it needed to be done.

The original wiring must have a signal converter (my mechanic called it a logic module I believe) because the turn signal only used the amber bulb and the brake only used the red. I did not want to take the time to figure out the signal converter so I hooked the turn signal and brake to both the amber and red lights. Not sure if this is legal but after being told by several drivers that my lights were not functioning I want plenty of light.

The lenses are quite fogged so I attempted to polish them with car polishing compound. Started with course, then fine. Helped some. Then I coated them with an interior plastic coating (like Armorall). They are a bit more bright.

Bob Miller, the 7 pin connector at the back of my Jeep Cherokee is factory installed, so I suppose that answers your questions?

My plans are to completely refurbish this trailer this winter so this wiring might be temporary. Or it might be sufficient to leave in place.

Thank you all for your help.

[mary and bob]

Surely someone here will scold you for having the amber functioning as stop lights, as I was LOL. I only use the red part of the lens, but have a second set of rear lights too. Plus some conspicuity tape on the bumper.

[ApothecaryJohn]

Hello, my wife and I recently purchased our first fiberglass camper, an 84 UHAUL ct 13. I am accessing everything and trying to address first things first. First, I need to fix the tail / turn and running lights. Does anyone have a wiring diagram. I checked the document area and couldn't find one. Also, which light / lense is used for what function, stop tail and turn etc. This trailer had been re-wired and if I'm going to re do it, I would like it to be right. Thanks in advance for any replies.

[mary and bob]

Join the Uhaul Facebook group, lots of info there. If your trailer has been rewired there's no telling how it was done, but basically the red part of the tail light is for tail and stop lights and the amber is for turn. Note that the amber part has a two filament bulb but only one is used for the turn lights, the other is not connected