Troubleshoot Vehicle Taillights Not Working with Tow Bar Diode Kit Installed When Plugged into RV

Updated 07/22/2020 | Published 04/10/2016

Question:

have installed universal wiring on my Jeep wrangler. have a 2003 jayco firenza. lights work on jeep until I plug into RV. then no jeep tail lights/brake lights/ turning signals.

asked by: Berkley

Expert Reply:

When you plug the tow bar wiring # 154-792-118158 into your tow vehicle the diodes of the kit will prevent the Jeep from having control of them if the signal from the tow vehicle is being applied. This is a function of the diodes designed to prevent the circuit from backfeeding onto the vehicle's wiring circuits.

If they are not working at all with the tow vehicle plugged in you will want to first verify that all the connections you made are secure. After that use a circuit tester to test the circuits that feed into the converter box and then make sure the appropriate circuit on the other side of the box is active as well with the circuit tester. You can test the input side of the diodes for this. Next test the output side of the diodes to ensure the voltage is passing through.

I attached a diagram that shows how this kit typically wires to a towed vehicle as well.

expert reply by: Jameson C

click to enlarge

Ronnie H.

7/13/2020

i have installed the Tow Ready Tail Light Isolating Diode System with 4-Pole Connector Item # TR118821 to my 2019 Jeep Cherokee Trail Hawk. All lights work correctly when the vehicle is unplugged from the Motor Home. However when it is connected to the MH everything works except the tail lights. I checked the 4 way flat from the from the MH to the rear where it connects to the 4way flat and it was good but still no tail lights. Am I missing something? I assume if all lights work during normal driving the the connections are correct. Thanks

Chris R.

7/18/2020

A lot of times issues like this can be caused by a weak ground. The first thing I would look at is making sure the white ground wire (with the ring terminal) from this kit is securely attached to a CLEAN, bare metal surface on the frame. If this is good check to ensure you're getting appropriate power from the motorhome - test its 4-Way to verify you're actually getting power on the running lights pin when those lights are illuminated.

Ronnie H.

7/18/2020

@ChrisR Hi Chris, I have already checked the 4 flat comming from the front of the jeep to where it plugs into the rear harness with a circuit tester and it is getting a good signal. The turn signal and brake lights work correctly so I would think the ground is ok but I will double check.

Ronnie H.

7/22/2020

@Roni have re-checked the ground and everything checked and both the turn signals and brake lights work but not the tail lights when hooked up to the MH. All lights work when not hooked to the MH.