How to troubleshoot a trailer wiring module

[Bill kubiak]

A few years ago I bought a trailer wiring kit from U-Haul for my 97 Jeep GC.
They take power from the battery to run the trailer lights and are expensive. They plug into the existing wiring with out making any splices etc.
Suddenly after 2 years only the left directional and left brake light is working.
U-Haul says the module probably failed and to buy a new kit 99.99.
Their stuff only carries a 90 day warranty.
Since they are the trailer experts I expected their product to last as long as the car did.
All the car lights work properly and they work thru the module since it is plugged right into the light systerm
Any thoughts how to trouble shoot to make sure it is the module and not somthing else

 

[Bondo]

Re: How to troubleshoot a trailer wiring module

Any thoughts how to trouble shoot to make sure it is the module and not somthing else

Ayuh,....

Grab a Test Light,+ see if there's Power at the terminals of the trailer Plug.....

If Not,...
Work your way Back.....
If there Is power,... It's the Trailer....

Btw,... Many places besides U-Haul sell those blinker converters.... Shop around...

 

[fdmsiv]

Re: How to troubleshoot a trailer wiring module

I bought my truck and it had a U-haul hack job done to the module. Get under your truck and double check the wiring connections. I would replace all of the clip jumper connectors U-haul put in with good crimp-on connectors.

 

[marquette]

Re: How to troubleshoot a trailer wiring module

if you buy one of the light up plugs that go into your wiring harnes where your trailer plugs in it makes trouble shooting go a little easier because you can easily see which circuits are working without having to hook up your trailer or hold a test lght or meter in place. they cost about $5-8 dollars depending on where you buy it. NAPA vs Wallyworld. you shouldn't have to pay more than $35 for a new module. try TSC, Fleet Farm or Autozone i think they all carry Lightmate.
a

 

[180shabah]

Re: How to troubleshoot a trailer wiring module

Is this the device installed on your truck???

It is only $40 from uhaul, and is certainly not your only option.

 

[timdan94]

Re: How to troubleshoot a trailer wiring module

I know the local autoparts stores carry them. I usually buy from hitchfinder they had one for my gf's forester with the plug and it was under $40

 

[Silvertip]

Re: How to troubleshoot a trailer wiring module

Have you checked the right side bulb on the trailer? That module can be working perfectly -- but if a trailer light or its wiring has a problem, obviously the light won't work. Can't blame the module for that. You have several other options for testing. A simple test plug which was already mentioned, using a voltmeter to see if you have voltage at all of the trailer connector terminals, or using a simple test light to perform the same tests.

 

[gstanton]

Re: How to troubleshoot a trailer wiring module

Make sure that any tester you purchase is 12 V and not 110V.

I work part-time in a hardware store and this is a common mistake!

 

[Bill kubiak]

Re: How to troubleshoot a trailer wiring module

That item in the picture is not what I have, mine was made specificaly for 93-98 Jeep Grand Cherokee. It has green test lights built into the connector plug. All the lights on the car work perfect.
My car has all these computers and information centers and the owners manual says not to use any trailer light kit unless it draws it's power straight from the battery, and it warns against splicing into the cars wiring system which is what I always did.
At first I thought the ground was bad becuase I know about 98% of all trailer light problems are caused by a bad ground. The module is solid state, I cannot imagine anything going wrong inside that, I just hate to buy another unit, if this can be fixed

 

[sundowner205]

Re: How to troubleshoot a trailer wiring module

Have you checked the right side bulb on the trailer? That module can be working perfectly -- but if a trailer light or its wiring has a problem, obviously the light won't work. Can't blame the module for that.

That is 100% correct. I have the same type of harness, and had a rear brake light go out; just one of the elements from an 1157 bulb. The result was the opposite side light on the trailer would not work at all. I changed the bulb and everything went back to normal.

 

[reelfishin]

Re: How to troubleshoot a trailer wiring module

The way those systems work is that it acts as a relay using a solid state circuit to run the lights off of direct battery power. It does use the vehicles light circuit to trip the 'relay' circuit though. This drain on the light circuit is very minor and not enough to affect the factory light module. (A bulb out warning or other lighting module codes would show any such problems).

I have seen several of those modules fail, but usually its caused by a short in the trailer which overheats the internal circuitry of the module.
A bad ground can also take out a module, as can age and water intrusion if the module was to get wet. Any vehicle with a light module or separate tail light and turn signal bulbs must use one of these, the difference is that on vehicles with an internal lighting computer or module, the power must come from the battery and not the factory lighting harness.

Take a test light and varify that you are not getting the right voltage to the trailer connector, this will make sure that we are chasing the right problem.

Then I'd also take a 12V source and test the trailer itself, if it works OK, then deal with only the truck. Connect the white wire to a 12 Neg. source, and then probe each of the other wires with 12V positive power and check the lights, Yellow will be left turn and brake, Green will be right turn and brake, and brown will be the taillights and marker lights. If the trailer is fine, go on to the truck.
Make sure the wires from the battery are supplying both 12V and that the ground supplying the module is good. It needs to have good input power and ground to work. Then make sure all of the input side wires are feeding the module, double check all connections. Chances are it's a bad connection rather than a bad module if the trailer is OK.

 

[Bill kubiak]

Re: How to troubleshoot a trailer wiring module

Did a lot of looking and checking and found some unusual things
The power wire from the battery terminal to the trailer lights was loose, had a new battery installed by sears, guess they forgot to tighten that connection, but the power was going to the trailer anyway.
Found a splice under the gas tank where the power wire connected to the lead from the module and it was all corroded and appeared to be burned through in several places, yet the power went thru.
Tightened up the loose wire and replaced the splice, still did not work.

Installed my trailer test light in the plug and tapped on the module, suddenly I got the tail lights to work, but after a while they went off again, more tapping and moving the wires at the plug in connectors and I got the right directional to work as well as the tail lights. turned the key off then back on the lights were inop again, gave up and got a cold one and went to the colonel for dinner, that where stand right now, any thoughts?????

 

[old & wise]

Re: How to troubleshoot a trailer wiring module

Been there, done that! Hope the chicken was good, cause your Uhaul module isn't! Had same exact thing happen, and found other identical complaints around the www.
In my case, the original installer ran the right side wires between OEM taillight grommet & body - metal chassis eventually shorted through the insulation & caused module to go bye bye.
The upside, when you purchase your new module, you can splice it right into the existing wires at the same location (if they're in good shape) - make sure you check them before connecting power.
Good luck,
J

 

[Ciera2450]

Re: How to troubleshoot a trailer wiring module

Thread is from 2008. I hope he's got it figured out by now! lol

 

[old & wise]

Re: How to troubleshoot a trailer wiring module

Yea, I figured I'd post just for the benefit of anyone else looking - I remember when I was having trouble & info was scarce.
J