U-Haul taillight voodoo - Fiberglass RV


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Old 04-04-2012, 07:34 PM   #1
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U-Haul taillight voodoo

I've been restoring a U-Haul 16' VT over the last six weeks, and was getting ready to take it on the road.

Apparently I did not determine that there was some dysfunction in the taillights when I drove it home. The entire assembly (both sides) lights up when the right turn signal is turned on, but the left turn seems to be functioning properly. The running lights appear to be out as well.

My question is this: My tow vehicle (1995 Toyota 4Runner w 3L/V6) is equipped with a Tekonsha electric brake controller that was professionally installed. Since the U-Haul only has an inertial brake system, is it possible that the extra line for the electric brake controller is sending a conflicting additional signal that is causing the problem? I'm trying to find a schematic for the Tekonsha 7-pin plug socket on the hitch as well to attempt to disable this temporarily.

Thanks!

Jonathan
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Old 04-04-2012, 07:48 PM   #2
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My only suggestion would be to check each connector position on the TV and compare to the interfacing pin on the trailer. It may be just wired wrong.

My UHaul wiring was all messed up when I bought it.

Are you using the amber lights at all?
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Old 04-04-2012, 07:59 PM   #3
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Hummm. I don't have a U-Haul, but I thought the 7-pin on the car end was "generic." IF, that is a correct assumption, see this: Fiberglass RV - Document Center - WiringDiagram_7-Pin_CarEnd

this is the trailer end: http://www.fiberglassrv.com/forums/d...?do=file&id=94
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Old 04-04-2012, 07:59 PM   #4
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By the TV, I assume you mean the female socket on the hitch. I'm in the process of downloading the tech manual from Tekonsha right now, hopefully that has a schematic that was followed for installation.

From what I can see, there was some pretty creative wiring done to this rig as well, so I have to question that. I'm not anticipating using the ambers up high if that's what you are asking, at least for this trip, I will probably only be day driving.
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Old 04-04-2012, 08:01 PM   #5
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Quote:
Originally Posted by Donna D. View Post
Hummm. I don't have a U-Haul, but I thought the 7-pin on the car end was "generic." IF, that is a correct assumption, see this: Fiberglass RV - Document Center - WiringDiagram_7-Pin_CarEnd

this is the trailer end: Fiberglass RV - Document Center - WiringDiagram_7-Pin_TrailerEnd
Thanks, Donna!
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Old 04-04-2012, 08:08 PM   #6
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U-Haul Tailight VooDoo

I would place a ground jumper wire from the TV to the trailer prior to going through all the tracing work. A poor ground will cause unusual problems/symptoms.
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Old 04-04-2012, 08:20 PM   #7
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Donna is right that there is a standard for which pin is wired for which function.

I thought that it might be a time saver to quickly map out the function of each pin on each end of the connector on your vehicle and trailer for diagnostic purposes. That way you know if it is wired correctly and also that each pin is getting a proper connection.

On my UHaul the grounds underneath were all corroded and the tail lights were not plugged into the proper powered wires. Each tail light has 5 wires - one ground and a red and black lead from both the upper amber and lower red lights.

UHaul uses four wires in a rubber sheath on each side. On mine black was tail lights, green brake lights and white was turn signal. A second wire picks up the ground from the frame and is tan in color.

Hope this is of some help.
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Old 04-04-2012, 08:43 PM   #8
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Hmm. Interesting that the schematic that Donna linked has the keyway on the bottom. Again, this wired socket on the hitch is being referred to as a "TV" here?

I disassembled the male plug on the trailer, and the Blue wire at position #2 is disconnected (and not even evident in the whole harness...), which makes sense, and I guess takes out the potential that the electric brake controller is causing a problem. Thanks everybody!
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Old 04-04-2012, 09:14 PM   #9
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i think most uhauls were orig 6 wire and set up to use the amber rears as signals like cars were doing at the time. napa sells an adapter to bring that across to & wire. I know because I had one when I towed mine home from Mich with a 7wire truck and it worked fine.
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Old 04-04-2012, 10:03 PM   #10
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TV is Tow vehicle. I replaced the original Uhaul wiring from the tongue up into the rear of the body to the tail lights with the four wire flat stuff. New wire is run to the right tail light, across the rear to the left tail lights, and along the left side to under the sink to tap into the marker lights. The marker lights are on two separate lines so there is a wire on the right to feed them too. I forget just how it was, but something like one wire fed the right markers, and the other wire was the left side and rear center three lights. I'm not using the amber part of the lights, but I have a rear bike rack that has tail stop turn lights on it, so that's four rear lights, plus some DOT conspicuity tape on the bumper and bike rack.
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Old 04-05-2012, 02:50 AM   #11
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Cool Why are things never simple?

Different manufacterers use different colors plus changing from 4 pin to 6 pin to 7 pin may also cause color changes:

Trailer and Towed light hookups

The 7 pin seems to agree on this one:

7,6,4 Way Wiring Diagrams

I guess the only thing to do is like suggested in the first link: Always check that your wiring is what you think it is before connecting.

I used to work in electrical design. The designs always looked really good and went together really well - until you turned on the electricity and something smoked. LOL

I found this paragraph most disturbing:

"Caution if your vehicle has a diagnostic indicator that tells you when a lamp is burned out or not functioning, you may need special wiring adapters and testers. Not using these adapters may cause damage to the vehicle wiring or computer."
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Old 04-05-2012, 03:15 AM   #12
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Quote:
Originally Posted by Jonathan Wright View Post
Apparently I did not determine that there was some dysfunction in the taillights when I drove it home. The entire assembly (both sides) lights up when the right turn signal is turned on, but the left turn seems to be functioning properly. The running lights appear to be out as well.
Jonathan
This sounds like a problem I fixed about 1963.

I remember fixing the left front directional on a '59 Ford. When the left turn signal was turned on, both parking/directional lights in the front came on dimly.
The right turn signal functioned normally.
The parking lights functioned normally.
What was bad was the ground for the left turn signal/parking light fixture.
What was happening was the power was going to the left turn signal light and since it had no ground after exiting the light, it traveled through the fixture ground, 'backwards' through that parking light, through the parking light wiring, through the right parking light and to ground there.
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Old 04-05-2012, 07:22 AM   #13
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I agree that bad grounds cause many, if not most lighting problems. It is pretty easy to just run a separate ground wire from the trailer tongue to the tail lights, underneath the trailer.

I'm doing this anyway, as I'm installing beefy wires to charge the battery from the tow vehicle.
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Old 04-07-2012, 03:47 PM   #14
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I've ended up doing an end run around the whole deal, running wiring directly to the lighting outside the carriage under the vehicle after mapping the plugs. I've used small diameter PCV pipe as conduit, and had to wire the green common between both sets of lights, with red and brown for left and right. There was an issue with polarity to make the lights function in the correct sequence for braking, turn and running functions. I think I'm good to go, now do get some brake and hub service done and I'll be on the road. Thanks to everyone for the input!
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