Weak Voltage on Right Hand Trailer Turn Signal Circuit

Updated 08/28/2018 | Published 08/27/2018

Products Featured in This Question

Digital Multimeter with 42" Long Test Leads - LED Display

(3)

$22.17

ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit

(522)

$192.62

Question:

I really hope you guys can help a fellow out. The right turn signal suddenly stopped working on my utility trailer. I suspected the trailer wiring so I replaced the entire harness and the lights. I ran independent grounds from the trailers four pin flat connector white wire to each light because I dont like grounding problems! Problem remains unchanged. I then rigged up a test light using one of the trailer bulbs testing each of the outputs on the cars harness. Turns out that the cars harness works well on every function except the right turn signal output at that pin green wire, the bulb blinks very dimly on the one filament and it wont even light up the other filament. Appears to me that the voltage coming out of the SMT module is too low to light the bulb. I checked all of the wiring from where the harness taps into the cars wires and I can find no defects they were soldered when the harness was installed. I could find no defects in the wires to the module or from the module. Is it possible that the SMT module has malfunctioned? I dont know what to do next in terms of troubleshooting short of cutting into the cars turn signal wire to test the output there. But Id prefer not to do that! Suggestions on what to do next would be so helpful!

asked by: Eric

Helpful Expert Reply:

The next set of troubleshooting steps for you are going to require access to a multimeter like part # PT89ZR. Once you obtain the multimeter you are going to want to test the right turn signal circuit at the trailer connector on the vehicle and compare that to the left turn signal circuit. If there is a drop in voltage present you will need to do the same thing but at the back of the trailer connector. If no drop in voltage is detected then the trailer connector will need to be replaced. If you do detect a drop in voltage then the issue is further up the line.

Now, I don't know if you have an aftermarket wiring harness or not but if you do then there should be a converter box in which you will need to test with the multimeter using the same steps above as listed for the trailer connector. If there is an issue with the wires that come out of the converter box and not entering then you know the converter box is bad. If there is no issue with a drop in voltage up to this point then there is something further along the harness that is causing the problem which is likely a short.

If you cannot or do not wish to dig further into the vehicle's trailer wiring harness then the easiest option would be to just install a new trailer wiring harness like the Tekonsha ZCI ModuLite Circuit Protected Vehicle Wiring Harness part # 119250KIT.

expert reply by: Conner L