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Discussion Starter · #1 ·
Hope you all can help. I added a brake light diode kit (RM-88400) to prevent the brake lights from coming on when the truck is switched off. Removed the brake light fuse, and put the kit in as instructed. Worked as it should … the brakes lights now won't come on when the vehicle is off, but will come on when the vehicle is in accessories or running. This is needed to prevent the truck brake lights overriding the signal from the motorhome when the brakes are pressed in the motorhome (which with the brake kit for the truck, it also presses the truck brakes at the same time thus turning on the truck brake lights -- the kit prevents this). Thus the truck won't override the signal from the motorhome.

Here's my problem, after install, and reinserting the brake light fuse, everything works as it should. But now I can't get the truck out of park!! Runs fine, but won't let me release the park button to pull out of park. Page 210 of the owners manual talks about Brake Shift Interlock and indicates if to override it, you must remove a rubber mat between the shifter and the cup holders. Then further tells you to press the white brake shift interlock lever (on the passenger side of the shifter assembly) forward while pulling the shift lever out of park (with brake pressed).

Question: Has anyone ever had to do this? Was this caused by removing the fuse and it confused the computer? If I do the above process, will it just reset or will it create further problems? I ask that last question as the owners manual indicates if the process is used contact your dealer as soon as possible.

Thanks in advance ….
 

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@Milehghcty - don't have any experience with this kit, but I do have an electronics background so we can try to talk this out...

By RM-88400, I assume you mean this Brake Relay Kit?
Roadmaster Brake-Lite Relay Kit for Towed Vehicles (Item # RM-88400)

If so, then I found this schematic online for Instruction Sheet A (Normally Open Install)
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A diode (only allows current flow in one direction) is much different electrical device than a relay (powered switch) so let's make sure we are talking about the same RM-88400 kit.

Can we ask what ignition-only powered fuse that you tapped into?
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Discussion Starter · #3 · (Edited)
Thanks jmperlik. Really appreciate you taking the time to try and talk this out. You have identified the kit; however, with the push button start, you use the blue wire versus the green wire used for a keyed switch. But other than that, it's the same wiring diagram. There were 4 wires coming off the brake light switch. The wire I used was the white/purple wire. The only wire that showed 12v when the brake was pushed. The blue wire from the kit was attached to the wire coming from the switch, and the black wire from the kit was attached to the other end that goes to the brake lights.

The switched fuse I used was the other fuse box on the passenger side under the hood and I used #37. I did remove the #14/15 (3 prong fuse) from the fuse box you show, which was the fuse for the brake light switch and datalink connector … I had this fuse removed while I was working with the brake light switch to prevent any issues.

I used a micro fuse tap for the fuse #37 under the hood and did validate that it was a switched fuse.

I did do the override of the Brake Shift Interlock as indicated by the owners manual that I described above and all works fine; however, once I put back in park you have to do the override lever again to get it out of park. It's real simple to do, but don't want to do this forever. Brake lights (in fact all lights) do still work, so strange that the Shift Interlock won't release.

I'm thinking about reconnecting the brake light wire (remove the blue and black kit wires) and see if solves my problem. But haven't had a chance to try yet. I've read other forums and heard of folks disconnecting their battery for several hours to reset everything … haven't tried this yet as not sure if it will cause other issues.

Thanks again. Hopefully I don't have to take to the dealer to resolve … I'm sure that will be on my dime vs warranty!
 

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Discussion Starter · #4 ·
I did get a hold of Roadmaster today and they indicated that the hotwire (red) should not be tied into the fuse panel, rather it should be tied into the hot tail light line from the motorhome. Thus when the MH is hooked up, you must run your MH lights which will affect the diode in the kit which doesn't allow the truck brakes to override the MH brake/turn signal lights. This is getting complicated and think I'll just pull the brake light fuse (#14) when I'm towing the truck. Roadmaster confirmed this would also work. Just one more step I was trying to avert, and really didn't want to run with the lights on all the time in the MH. Wish I would have called before I started this project … would have saved me a lot of time.

I did pull the red wire (for this RM-88400 kit) from the fuse box and all works now. Shifts in/out of park. So at least that is no longer the problem. I followed the instructions from a youtube etrailer video, but the video wasn't correct for a push button start!!

Thanks jmperlik for trying to help with this problem … but not a problem any more.
 

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@Milehghcty - OK, so the red wire that the schematic shows plugging into the fuse box, doesn't plug into the fuse box? Wha what?!?

I dug a little deeper and found the actual product Installation Instructions online:

Brake-Lite Relay part number 88400 Installation Instructions

and now see what you are talking about:
  • Instruction Sheet "A" - If the vehicle starts with an ignition key, use the ‘A' instructions_ (Normally Open Install = w/Ignition Key)
  • Instruction Sheet "B" - If the vehicle has a push button ignition, use the ‘B' instructions (Normally Closed Install = w/Push-button Ignition or neutral tow kit)
and Instruction Sheet "B" has a completely different schematic diagram for Normally Closed Install:
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that shows:
  1. Red wire going to the RV brake light circuit as you describe
  2. Brake diode you referred to in your original post (Roadmaster Part # RM-790)
Now that I have dug deeper, I realize that both of the color schematics I posted are mark-ups from the e-trailer website of the Black-and-White schematics from the Brake-Lite Relay Part #88400 Installation Instructions PDF link above = I guess I should have scrolled down a little further when I found this product on the e-trailer website...

Good info for the next owner who attempt this install = hopefully you'll save them a lot of grief & effort!
 
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