Tow lights for toad vehicle don't work if headlights are on

[johnlantz]

We have a class C and a Jeep that we tow behind. I just noticed today when hooking up the vehicle that the lights (brakes and turn signals) on the tow vehicle do not work if the headlights are on in the RV.

If the headlights are off on the RV, everything (turn signals and brakes) works fine on the tow vehicle. If the headlights are on in the RV, the parking lights are on in the tow vehicle, but the brakes and turn signals don't work.

Any ideas is this something wrong with the wiring on the RV or the wiring in the tow vehicle? We just got a new tow vehicle this year. But I never bothered to check the hookups in the past with the RV headlights on. It may have been like this with the old tow vehicle and I never knew it.

[SeaDog]

What about when you only have the parking lights on on the RV do the lights on the Jeep still work correctly?

[emm-dee]

The parking lights on the toad shouldn’t be on at any time, just the rear running and brake lights. What kind of harness did you put in the Jeep?

[johnlantz]

Not sure what the difference is between parking lights and running lights. Maybe we are talking about the same thing.

The harness that was put in the Jeep is this.
https://www.amazon.com/Blue-Ox-BX882...25710767&psc=1

[johnlantz]

Originally Posted by SeaDog

What about when you only have the parking lights on on the RV do the lights on the Jeep still work correctly?

I did not try that. I will go over this week and give that a try.

I'm just trying to figure out do I take it to the place that wired the Jeep and tell them something is wrong with that wiring? Or take it to a RV place near me and have them look at the RV. Unfortunately the place where the car was wired is much further away.

[emm-dee]

Originally Posted by johnlantz

Not sure what the difference is between parking lights and running lights. Maybe we are talking about the same thing.

The harness that was put in the Jeep is this.
https://www.amazon.com/Blue-Ox-BX882...25710767&psc=1

That’s only the connector cable between the RV and the Jeep. Once it connects you have to have something like this:

https://www.amazon.com/Hopkins-56200...gateway&sr=8-1

That setup illuminates only the two taillight/brake/signal lights on the rear of the Jeep. That’s all you need.

[johnlantz]

Originally Posted by emm-dee

That’s only the connector cable between the RV and the Jeep. Once it connects you have to have something like this:

https://www.amazon.com/Hopkins-56200...gateway&sr=8-1

That setup illuminates only the two taillight/brake/signal lights on the rear of the Jeep. That’s all you need.

I have no idea on what the wiring the place did when the rigged the car for towing It does illuminate the signals and brakes on the Jeep when I don't have the headlights on in the RV. But once I turn on the headlights in the RV, the turn signals and brake lights no longer work in the Jeep. Instead the tail lights are on in the Jeep. Not the brake light or turn signals.

Thanks for the input. I'll start with calling the place that rigged the car and see what they say. If it's not them, then i'll try the RV shop.

[emm-dee]

Originally Posted by johnlantz

I have no idea on what the wiring the place did when the rigged the car for towing It does illuminate the signals and brakes on the Jeep when I don't have the headlights on in the RV. But once I turn on the headlights in the RV, the turn signals and brake lights no longer work in the Jeep. Instead the tail lights are on in the Jeep. Not the brake light or turn signals.

Thanks for the input. I'll start with calling the place that rigged the car and see what they say. If it's not them, then i'll try the RV shop.

Easy answer. You have a bad installation in the Jeep.

[Fishtexx]

Check the ground connections.

[PenJoe]

Depending on which Jeep you have, there can be two wiring configurations. One is the #6 posting of a Hopkins kit. This wiring is integrated into the OEM wiring. For the second type, some Jeeps have space in their tail light assemblies to have a completely independent brake/turn/tail system. I used the second type with a Blue Ox kit installed on a 2012 Jeep Liberty.

Also, a bad ground will do some really weird things with lights. Your symptoms could be one of them. The Sunseeker, as most newer vehicles, is factory wired so that the headlights, tail/turn/brake brake lights are on different circuits that the 7-pin harness and they are fused separately.

The first picture you posted is called an umbilical. For the TV to the toad setup, it should be a 7-pin at the Sunseeker, and a 6-pin at the front of the Jeep. One of those wire activates with the ignition on the Sunseeker. It can be used to supply power for a battery tender on the toad battery.

[awellis3]

Originally Posted by Fishtexx

Check the ground connections.

Yup! Somehow the Jeep's tow wiring is grounding through the RV's headlights circuit.

[emm-dee]

This problem is illogical. When one turns on the parking lights, 12 volts DC is sent to pin #three at the vehicle seven pin connector. If you turn on the headlights, 12 volts DC is sent to pin #three at the vehicle seven pin connector. There is NO difference between the power output...it comes from a source which cannot be one or the other. In fact, turning on headlights also turns on parking lights, always. Turning on parking lights should never turn on headlights but will always supply power to pin three.

One needs to start at the seven pin connector and use a voltmeter to check the output at each pin.

The operation of the turn/brake lights is independent from the operation of the rear running lights. If the OP is losing brake lights when the headlights are on in the RV then the installation in the Jeep is wrong.

There’s a reason for using a special wiring setup to operate the Jeep lights because they have to remain independent of the RV. Power has to be isolated. What the OP is describing may cause serious electrical problems in the RV.

[HerveVR]

From what I have read in another forum.
Some year/model of Jeep requires a 《special》 Mopar cable for toad's lights when flat towing.
Check carefully in your Owner's guide.

[emm-dee]

Originally Posted by HerveVR

From what I have read in another forum.
Some year/model of Jeep requires a 《special》 Mopar cable for toad's lights when flat towing.
Check carefully in your Owner's guide.

ALL Jeeps and probably every other vehicle being towed require a special cable. Mopar has one if you want to pay the extra bucks. Hopkins and several others distribute the cables. Problems come up if the kits are not installed correctly, usually expensive problems.

[johnlantz]

Originally Posted by emm-dee

ALL Jeeps and probably every other vehicle being towed require a special cable. Mopar has one if you want to pay the extra bucks. Hopkins and several others distribute the cables. Problems come up if the kits are not installed correctly, usually expensive problems.

"ALL Jeeps and probably every other vehicle being towed require a special cable. ". This is confusing. What would a special cable be as opposed to any other cable that would be used for the toad?

[emm-dee]

Originally Posted by johnlantz

"ALL Jeeps and probably every other vehicle being towed require a special cable. ". This is confusing. What would a special cable be as opposed to any other cable that would be used for the toad?

Yep, need to be more specific. The cable from the TV to the toad is pretty normal, usually four wire for basic lights, five wire for lights and brakes and six wire for lights, brakes and battery charge.

The cable I was referring to is AFTER the front connection to the RV. Just running any old wire between the, ie, RV running light output, will cause problems if connected directly. Special cables (or installation kits, etc) will have diodes etc to prevent the toad from feeding electricity back to the RV. They have some other PFM functions that are basically not needed to know about but nonetheless very important.