2026 Montana 290RL: No Brakes or Signal Lights

[wicked2]

Have had the trailer since April. The amount of problems experienced in 3 trips have been staggering. But not until we lost our trailer brakes, brake lights and turn signals did the problems reach a safety issue. We cannot even tow it down the road legally to get home. The giggy box is wired correctly so the problem now is the wiring harness in underbelly. Completely at a loss!!!

 

[Carl n Susan]

The Giggy box is independent of the brakes, brake lights and turn signals.

I assume you have checked for voltage at the 7 pin connector. How about at the 4" square box on the pin where the umbilical cord connects? The lines in question then run from there directly to the fixtures as I recall.

 

[ChuckS]

If your RV has the Lippert ABS ( cant tell cause no year in your signiture ) then you might want to eyeball this info:

Yes, a malfunctioning or disconnected Lippert ABS module can absolutely cause you to lose all brake lights and turn signals on your Keystone Montana fifth wheel.
The Lippert Trailer ABS utilizes a pass-through wiring harness system, meaning your truck's lighting and signal circuits run directly into and through the main ABS control module before traveling to the rear of the RV.
If there is a failure in this module or its connections, the entire circuit is interrupted.

Common ABS-Related Causes

• Loose or Disconnected Main Harness Plug: This is the most common culprit. The locking tabs on the heavy wiring harness plug going into the ABS module can crack or break from road vibration. If the plug backs out even slightly, you will instantly lose the turn signals, brake lights, and electrical trailer braking functions.
• Damaged or Pinched Axle Wiring: Because the harness routes under the chassis around the suspension area, hitting severe bumps or road debris can pinch or tear the wires leading to the module.
• Internal Module Failure: While less common, an internal electronic failure inside the module can block the pass-through signals from reaching your rear lights.

Where to Find the Module & How to Troubleshoot

1. Locate the ABS Module: On most fifth wheels, the Lippert ABS module is mounted directly to the inside of the frame rail, usually on the driver's side within a foot of the front axle. Look for a small black electronic box with several heavy cable bundles plugged into it. You may need to pull back a small portion of the underbelly coroplast to access it.
2. Inspect the Connectors: Ensure the main power and lighting harness is pushed tightly into the module and that the plastic locking clip is fully engaged. Look for any unseated red weather seals or bent connector pins inside the plug.
3. Rule Out the Truck Fuses First: Before dropping the underbelly pan, use a 12V test light or multimeter at your truck’s 7-pin bumper connector to verify that the truck is actually outputting the turn and brake light voltages. Trucks use isolated, dedicated fuses for trailer tow circuits that frequently blow independently of the truck's own lights.

Link to Service manual and I would do the power reset first on the ABS module:

https://lci-support-doc.s3.amazonaws.com/manuals/brakes/ccd-0006506.pdf

 

[Carl n Susan]

If your RV has the Lippert ABS ( cant tell cause no year in your signiture ) then you might want to eyeball this info:

They have a 2026 model according to the Title of the Thread.

 

[ChuckS]

They have a 2026 model according to the Title of the Thread.

Old eyes here.... Yup I see it now in the Title....

 

[DutchmenSport]

Don't know what all diagnostics you've preformed, but the umbilical cord that plugs into the truck...

Follow the cord to the location where it attaches to the camper.

On mine, there is a metal box under the over-hang where the umbilical cord attaches to the trailer. On mine, it's just a simple house-hold aluminum junction box with a cover.

When our camper was new, I had a similar problem, but I did not loose ALL those lights. I felt pretty certain the problem was not with the truck.

When I removed that cover, I found out the wires were simply twisted together to connecting wires for the trailer, and several of them had pulled loose from each other. I was able to reconnect them, used a bit of solder to hold them together, put new wire nuts and tape on them and never had a problem again.

That's an easy item to check if you have not done so yet.

Good luck.

 

[EGR & GSR]

Have had the trailer since April. The amount of problems experienced in 3 trips have been staggering. But not until we lost our trailer brakes, brake lights and turn signals did the problems reach a safety issue. We cannot even tow it down the road legally to get home. The giggy box is wired correctly so the problem now is the wiring harness in underbelly. Completely at a loss!!!

I had same problem with 2027 3100 RL the wiring harness on ABS control box had come out . Ended up having to replace wiring harness because locking tab was broken. Was on side of road a long time checking everything not knowing about the abs system.

 

[Lcwl]

What is your tow vehicle. My F250 ford has a recall on losing trailer brakes and lights to your trailer

 

[Mark77]

Would be nice to know what he eventually figured out so others could learn...

 

[Dfb]

Like Carl has stated, check at the trucks connector.. If that is good Id be looking for a bad ground. I find it hard to believe you'd lose all the lights and brakes.. Check the ground at the connector ... If you have nothing at the connector, Id then check the combination switch at the steering wheel. Everything goes thru the switch.. Lights, signals, and since the brakes are electric most likely ran off the breaker lights that also goes thru the combo swich..

 

[Mark77]

OP has not visited in 2 weeks.

The days of TS and Brake lights running thru the TS switch are long gone. Everything is CAN now... all every switch in your vehicle does is tell a BCM (Body Control Module) what you want to happen and then the "computer" sends the message to yet another module somewhere else on the vehicle and eventually one of them turns on the power to make happen whatever the input wanted.

Fascinating really, and kind of complicated but troubleshooting is easier if you have the correct diagnostic tools. That's why they say SOME mechanics are really not mechanics anymore, but rather parts changers.

But I digress....

 

[RMcNeal]

Yeah, the CAN bus system kinda reminds me of the old token ring networking back in the day. Glad ethernet took over.