Troubleshooting Parking Tail Lights Staying On In 2025 Grand Cherokee After Flat Tow System Install

Updated 05/24/2026 | Published 05/21/2026

Products Featured in This Question

Roadmaster Single Park Light Diode

(133)

$22.24

Pollak 6-Pole, Round Pin, Plastic Wiring Socket w/ Rubber Boot - Vehicle End

(225)

$21.43

Question:

Hello, I have on order a RM-690 Park Light Diode. I recently moved all my toad equipment and installed a new base plate for my 25 Jeep Grand Cherokee Overland from you - nice base plate. I installed a charge line with a fuse in-line close to the battery post. Recently, after driving in the rain, my tail lights remained on in my garage. I pulled the fuse in the charge line, and they went off. Will this RM-690 provide me protection from the power back-feeding, or do I need the Auto reset fuse, and does it container the technology to prevent back-feeding? I am replacing with 6 way you shipped it yesterday along with the RM-690 - Is the RM690 the wrong part to put in-line for a charge line?

asked by: Mark W

Expert Reply:

Hi Mark; the # RM-690 diode can be used to prevent backfeeding on the affected circuit. It only allows power to flow in one direction, so if the issue was caused by voltage backfeed into the Jeep’s taillight circuit the diode will correct it. The auto-reset breaker/fuse is only there to protect the wiring from an overload condition, it does not prevent backfeeding.

Since the problem started after driving in rain, and you're already replacing the 6-way connector, there is a good chance the original socket had some moisture that caused the backfeed issue. If the charge line and taillight circuits somehow connected then power would transfer over. Replacing the 6-way may resolve the problem entirely, but adding the # RM-690 inline on the affected circuit is still a good safeguard against backfeeding.

Where are you headed once you finish your flat tow setup?

expert reply by: Robin H

Roadmaster Diode
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Mark W.

5/24/2026

Thank you for your reply (on a Sunday, holiday weekend) - headed to the Texas coast from Dallas to test the tow set up in 3 weeks. I've also read the Roadmaster 88400 may be needed for the 25 Jeep Grand Cherokee Overland to correct a brake light over-riding the blinker from the RM Invisibrake system when the brakes are applied. I believe I have also read that the Motorhome park lights will need to be in the on position for all of this to work with this kit installed. I did test this hooking up my Jeep to my wife's Lexus SUV, and the blinkers go solid when the brake is pressed (Motorhome is in shop now) Any other work around for this? - it is OK to answer me on Tuesday, I will pick up my motorhome later in the week, and need to know if it is OK to tow it back to my storage place (about 25 miles), or wait until I get this sorted out. Mark

Robin H.

5/24/2026

@MarkW you're welcome! I don't mind, I'll have tomorrow off (I think) and it helps when someone chips away at the weekend question pile. The # RM-88400 is designed to correct the exact brake light override issue you described on vehicles like yours using a system like the InvisiBrake. Since your testing showed the turn signals go solid when braking, it appears your Jeep may need it as well. You can likely tow it home, but until the relay kit is installed the brake lights may override the turn signals while braking, making the signals harder for other drivers to see.

Mark W.

5/24/2026

@RobinH, thank you, I will order one in a while - have a good weekend.