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Electrical damage can occur to the towed vehicle if its headlights are turned on while still connected to the motorhome. The Park Light Diode from Roadmaster will stop any interaction between the two park light systems, preventing electrical feedback and electrical damage.
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Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.
Today on this 2003 Jeep Wrangler, we're going to install part number RM-690. This is the Roadmaster Single Park Light Diode. The idea behind these diodes is to prevent any backfeed from the towed vehicle going up to the RV. Typically this is used on the running light circuit where the power from the towed vehicle will backfeed up into the RV. Now we're actually going to use it for a little bit different application. In this situation, our Jeep has a after-market supplemental braking system installed and it provides backfeed in that fashion. We need to install two diodes to prevent backfeed going up to the RV and we'll show you the problem at the front of our Jeep here. With our Jeep in tow mode running behind the RV, we'll go ahead and check with the brake pedal being pushed down.
Okay, we've got backfeed from the brake pedal, so we're going to go ahead and add the two diodes to our left turn and right turn circuits to prevent the backfeed going up to the RV. With this part number, you get the diode and two terminals for the ends. This basically works like a one-way valve. You get power coming in and then power coming out. Now, we're going to install this on the section of the towed vehicle wiring harness which means where our supplemental braking system attaches to this wire harness and then out to the tail lights where the diodes are out there. What we're going to do is split our wires up.
I'm going to make a long section. I'm going to spread it apart. We'll go ahead and cut our yellow wire here, strip back the ends just about a quarter inch or so. Now we'll go ahead and we'll temporarily put in our diode. We want our input from the RV only going out to our towed vehicle so I'll put the input towards the front. That other tab goes to the wires out back. We'll just leave this alone for now.
We'll permanently attach them as one of our last steps. Now we'll do the same thing on our green wire which will be our left turn signal and brake. These terminal ends are pretty tight so we may have to use a pair of needle-nosed pliers or wire strippers to help pull them apart. Okay, we've got them temporarily in place. We'll go ahead and try it out. Now we start off, when we push the brake pedal when the vehicle is in tow mode when it's activated by the supplemental braking system, we had power to these two poles which we did not need.
Now with our diodes in place, we'll go ahead and try it again by activating the brakes, and we have nothing, which is exactly what we want. Once we verify it's working the way we need it to, we can go ahead and secure our diodes. Before we secure our diodes, this is underneath the vehicle. We're going to encase the whole thing with some electrical tape and then we're going to go ahead and zip tie it to the side of our frame. Also on the back side of it, it has some adhesive on the back too so if you put this on the inside of the vehicle, you can simply attach it to the sheet metal on the inside and not worry about it. If you test this and find out that it's still not working right, all you got to do is just flip the diodes around and then try it again. We'll go ahead and zip tie our wires to the frame, and you definitely want some extra long zip ties for this or you can double stack a couple of zip ties too. With everything bundled up, that'll finish it for our install of part number RM-690 from Roadmaster, the Single Park Light Diode on our 2003 Jeep Wrangler. .
Just what we needed at a great price. Very fast shipping.
Thanks.
Great 'insurance' policy for any towed vehicle. It never fails... you get to your destination, you are tired, you jump in your towed vehicle and turn on the lights. Too late! The damage is done. If you haven't turned of the lights of your coach and your towed is hard wired to use it's own lighting as 'trailer' lighting, you NEED THIS DIODE. A breeze to install and a cheap failsafe .
I didn't quite use this for the intended purpose. I was having trouble with the hazard lights backfeeding the brake controller and pulsing the trailer brakes on my 1988 Chevy 1 ton pickup. Broke out the wiring diagrams and turns out on the squarbodies, that's how they wired the brake lights. Installed this diode after the brake light switch and brake controller but before the hazard switch. Solved the problem. The diode seems to be built well. The fact that it has blade terminals on it makes the installation easy. Very happy so far.
Very nice product. Completely sealed aluminum housing is high quality. It was just what I needed to prevent back feed on the battery charge wire between my towed jeep and motorhome.
My application is a little different. I had used a relay to feed battery voltage directly to the ignition coil on my 65 Corvair. The alternator warning light back fed from the battery causing the engine to keep running with the key off. I installed the diode in the line to the warning light. Problem solved. Great product. Easy to install and works as described.
Works as advertised
Came on time and did the trick
The diode does exactly what I need it to, and for which it was engineered and built.
Used for isolating the car battery from the trailer battery.
Used this in conjunction with a 12V charge line from my Class A motorhome to the battery in my Jeep to provide charge to battery when towing and using BrakeBuddy. Prevents backflow discharge when stopped. Also put in fuse at front of coach and fuse at Jeep battery as protection for 12V system in case of chaffed wire or grounding.
Greg S.
10/9/2018
Towed that Jeep to several places last year. Still works just like its supposed to.
I bought 3 diodes for my 09 Saturn that was back feeding to my RV. This took care of the problem. Easy is it to install and peace of mind that I won't have a problem now . Had I known I didn't hade diodes on my wiring harness I would install them at the same time .but buyer beware on buying other people's products not for E trailer .
Craigc
11/14/2016
Its been one year now and a diodes are still doing their job
Very fast and easy transition. My order was delivered quickly and on delivered on time. This is my first purchase from etrailer, and I plan to buy from them again.
The product will be used in the 12 volt output of a Motorhome trailer connector to feed a tow vehicle. The diode is rated at 85 amps which covers any need I might have. The construction of the diode is first rate.
Cbtraveler
12/19/2017
Product is still working fine without any problems
Just received today but worked as advertised! Thank you for the great customer service!
Works as described. I used it in the charge line from the motorhome to the towed vehicle battery (2012 CR-V, diode in from charge line, diode out to CR-V battery).
John F.
9/9/2020
It still works as intended with no problems.
I got a diode which is the item I ordered. The diode says its for parking lights. There are zero instructions. This is not helpful just charged me for a product and sent me on my way. Smh...
Nick S.
10/13/2025
I am sorry to hear there were no instructions in your package. For this diode what you will want to do is locate the wire that leads to the parking light bulb. You'll cut that wire and put it in-line with the wiring. The IN side will be the part of the wire that leads to the front of the vehicle. The OUT side is going to the bulb. I attached a video for you as well on a different vehicle to get a better idea of the process.
Product serves my application. Wanted to be sure that the break away emergency battery power on trailer brakes, when activated, would not back feed to my truck and damage factory brake controller.
Installed in 7 conductor cable between truck and trailer. Under test it works fine. Hope I never need it on the road. Recommend it for protection from back feed voltage. Could be used in any DC voltage system when the flow of current must be controlled or protected.
This product works exactly as desired. The packaging is excellent, and it did the trick. I'd definitely recommend it to prevent backfeeding.
I'm very happy with etrailer, their selection of products, pricing, and their information. They truly differentiate themselves with the value add, yet keep the cost competitive. Way to do business!
John O.
4/25/2018
One year later its still working as good as new! very happy with this product.
Pretty basic item here, it prevents current from going back and forth. And it does just that! Worked perfect for my situation on the living quarters gooseneck horse trailer. I had installed a new battery breakaway system that charges the battery when the trailer is plugged in to the truck. However in my case, when the trailer wasn't plugged into the truck, I was getting current back through the wiring harness from the house batteries that was charging the breakaway battery. Not good as over a short time period it would have drained the house batteries. This little item prevents that from happening. Thanks Guys!
Didn't know I needed this to wire my 7 pin connector for trailer brakes. My neighbor told me I would need it so I ordered it. It works great. I suggest you mention it when someone orders a 7 pin wiring harness for a newer car.
The road master diode worked perfect I used it as a battery isolater between my trailer winch battery and my trailer brake battery so when I would use the electric winch it doesn't drain my trailer brake battery with combination with a isolater switch so long u wire it correctly it works perfect.
Ronald
2/6/2022
This has worked great on my boat keeping my trolling battery charged while fish. It keeps it topped off.
I got this to isolate my emergency brake disconnect battery from the main trailer battery. I would have preferred if the included wire crimps were the heat shrink type. Shipping took forever and was not trackable. Otherwise, this was a super easy product to install. Thank you etrailer for making it easy!
I have a Class A Rv and it has a hydraulic pump on the brake lite switch. I was getting a back feed from the running light back to the pump. I installed this diode and it stopped the back feed. Works great and fast shipping from Etrailer. Thank you Ashley E. for all your help. I couldn't figure out what would solve this problem.
Does what it's supposed to do. My warning lights do not come on anymore. That being said, it should be included or recommended for the Tekonsha brake controller system. I guess all vehicles don't have that problem, but why take the chance. I have a 2017 Toyota Highlander Hybrid.
Fast free delivery, Installed very easily, works perfectly!
This product was installed to protect my roadmaster invisibrake system when using the Hopkins towed vehicle light kit on my 2015 Jeep Wrangler.
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Jacob
6/7/2025
The diode has been installed on my truck for a year now. Still working great. Still very happy with it.