trailer wiring problem

Shift518 Automotive
1

Today I wired up a trailer harness on my '05 Elantra. I had to use a converter because nobody makes a harness for my car. It turns 3 wires into 2.
On the input end:
-taillights
-brake lights
-left turn
-right turn

On the output end:
-taillights
-right turn and stop
-left turn and stop

Heres the issue-
When I connected the car end of the wiring to the trailer end I checked all the lights to make sure they worked.

The left and right turn signals and brake lights all work. However the taillights dont work. When I turn the lights on nothing works- the brake and/or turn signals stop working too.

I thought it was bad wiring on the trailer so I bought a new harness. Same problem.

Then I checked for voltage with a test light poked into the wires right up by the plug on the trailer- the test light lit up. Then I checked how much voltage with a voltmeter. Im getting a reading of 11.8- 12.1 volts with the taillights turned on so theyre getting power.

Then I figured it must be bad lights so I just bought new ones. Same fucking problem.

Whats the deal here? Why dont the taillights work even with the right voltage?

I want to be able to use the trailer this weekend but cant without taillights on it.

2

it’s hard to say without looking at it. I’m sure I can find the problem in under a minute though…

3

Ive been fucking with it for a few hours with no luck. Its gotta be something fairly simple and stupid but Im losing my mind trying to figure it out.

4

haha, my dad is having the same fucking problem with his wiring harness on his trailer… he just had a hitch put on his car too. my dad bought a new wiring harness from harbor freight and were gonna wire it up this weekend to see if it fixes his issues.

5

I thought it wouldve fixed mine but it didnt. :headbang

6

the harness on our trailer is fucked… its frayed in a few spots and shit.

7

ground?

8

grounded it is.

9

I grounded the harness to the same spot I was grounding the test light.

The turn signals and brake lights work even without being grounded though.

10

we had the same problem with one of our trucks, i dont remember what i did to fix it, i think i had to run a small jumper wire inside the trailer plug maybe?

11

sounds like you have a short to ground, make sure you’re wiring is correct before you set you car up in flames.

most trailers are ground to chassis, white brown, yellow green. white is ground, brown is running lights positive, green and yellow and brake/turn illumination positive. What I mean is typically power in through brown/green/yellow via wires to the bulbs and then the bulbs ground to the trailer chassis back to white and back into the car. Again sounds like short to ground/backfeed.

be sure that the power/ground coming out of your car side harness matches up with that corresponding setup. bust out the DVOM and verify. are your trailer light 1197 bulbs(dual filament for separate running and brake/turn) or single filament 1156?

conversion plugs are worthless, unless converting a 4 wire railer to run off 7 wire brake plug. best to wire the car in hardlink with a proper harness. ask Clark…just had to rewire his 7 wire e-brake trailer for racing a couple weeks back…

12

did u have to completely run the wires, or where they there and u just 2 add your adapter?

13

Im running the converter because nobody makes a wiring harness for my car. There wasnt any trailer wiring already in the car. The converter is hardwired to my taillight harness- not a plug in.
Its like this:
http://www.etrailer.com/pc-ELEB~118175KIT.htm

The main bulbs are 1157’s. Theres also a smaller bulb on each side but I didnt check the number on them.

I had 12 volts at the end of the wiring just before it goes into the lights with the taillights on.

The end of the car harness matches the end of the trailer harness.

I had this problem with two different trailer harnesses so I dont think anything is shorting out.

I was really hoping to use the trailer this weekend but cant without taillights on it. :wtf

14

well i can tell you right now that if you bought a kit like that link it’s the wrong one for your trailer. that’s meant for 1156 not 1157 dual filament. make sure you have the right system

15

One of my friends figured it out- the taillights themselves need a ground.

I ended up running another ground wire from the left taillight to the tongue of the trailer and everything works.

I couldnt get a good ground anywhere else on the trailer.