Momentum Brake wiring routing from pinbox into Generator bay

DRedmond

Member
Joined
Aug 6, 2022
Messages
23
I want all the brakes I can get short of a disc conversion; 2021 351M. Considering an independent wire run to each wheel with 14ga jacketed pair. What is the collective wisdom on routing the new wires from the pinbox junction and 7-pin connector? The stock harness appears to route through the frame members, I want to ensure I don't run them in a hidden path without effectively protecting the wires. I cannot see any wire chase to pull the wires through. From there, I can get the 4 pairs in the underbelly and to each wheel.

Best I can see, the 'right' way to do it is dropping the aluminum body panel under the overhang to get to the frame - ain't happening. Or, go up through the floor into the under-bed storage then back down into the generator bay with some sort of conduit to protect the wire.

Anybody have experience with this?
 
I ran a new wire from pin box back in my 399. I used 12 awg marine grade wire and ran it in a wire loom along the frame rail to the brakes. I also used the 12 awg wire to go between both sides of each axle.
 
I want all the brakes I can get short of a disc conversion; 2021 351M. Considering an independent wire run to each wheel with 14ga jacketed pair. What is the collective wisdom on routing the new wires from the pinbox junction and 7-pin connector? The stock harness appears to route through the frame members, I want to ensure I don't run them in a hidden path without effectively protecting the wires. I cannot see any wire chase to pull the wires through. From there, I can get the 4 pairs in the underbelly and to each wheel.

Best I can see, the 'right' way to do it is dropping the aluminum body panel under the overhang to get to the frame - ain't happening. Or, go up through the floor into the under-bed storage then back down into the generator bay with some sort of conduit to protect the wire.

Anybody have experience with this?
I've considered doing the same thing with 12 gauge wire, but after looking at your suggestion, I think 14 gauge wire to each brake from a common starting point would be sufficient. I haven't done it, and would be very interested in your experience, especially figuring out where the actual trigger wire is at the battery. Each brake would likely pull a max of 4-5 amps, so 14 gauge to each brake would be fine, but IMO, if they were daisy-chained, it could be iffy.

Please post back or PM me with your findings. I also would like max braking force. I've been lax and haven't even checked what I'm pulling now with regards to amperage at each wheel/brake.

TIA.
 
As per Dexter Service/Maint manual, each brake coil magnet pulls 3A maximum....so you really don't need very heavy gauge wire for that. The reason for the 12ga wire up front is because it carries all of the brake current (4 wheels or 6 wheels) until it splits/parallels off to the individual wheels.
 
From what I've read, 12" brakes may draw 4 amps, or all four could show 15-16.3 amps. The 7" brakes will be at about 3.2 amps, or all four around 12.6-13.7 amps.

FWIW, I just came back in from using a clamp on amp meter, and with the gain at the truck set to 10, I show from 1.47 to 1.63 amps on the four wheels, with the driver's side showing 1.57 and 1.63 amps, and the passenger's side showing 1.47 amps on both wheels. Not exactly what I'd hoped to see. Also there were two different sizes of wire, some looked like 12 gauge and some like 14 gauge.
 
From what I've read, 12" brakes may draw 4 amps, or all four could show 15-16.3 amps. The 7" brakes will be at about 3.2 amps, or all four around 12.6-13.7 amps.

FWIW, I just came back in from using a clamp on amp meter, and with the gain at the truck set to 10, I show from 1.47 to 1.63 amps on the four wheels, with the driver's side showing 1.57 and 1.63 amps, and the passenger's side showing 1.47 amps on both wheels. Not exactly what I'd hoped to see. Also there were two different sizes of wire, some looked like 12 gauge and some like 14 gauge.

Do you have Dexter axles? That is what my reference above in post #4 was for.....and again, taken directly from the Dexter service/maint. book. I do remember seeing also that when testing, the truck's engine should be running. Yours looks to be about half of what it should be. Did you happen to take a voltage reading on the individual coils while you were under there?
 
Yes, my axles are Dexter, and it would appear that Dexter is the only site that says 3 amps is the max, but they also mentioned nothing about checking with a clamp on amp meter. All other sites having to do with trailer braking and trailers in general, cite 12" brakes as 4 amps or a bit more. Go figure.

I did have the truck running, and the gain maxed out on the brake controller. No, no voltage reading, no easy access to a bare wire for that. I'm plugged in to shore power, so low voltage really shouldn't be an issue. But nothing is guaranteed. :) We're going to be out and about for the next month, month and a half, so I can't do any in depth searching for the wiring for the brakes. I thought I could trace it down from the connection box from the truck, but it hooks a right out of the box and disappears behind fiberglass and insulation. Bummer. I'm going to keep an eye on this thread, and really dig into this over the winter downtime.

Any advice, hints, or "Hey Dummy!" you can send my way is appreciated. :)

We'll be up in Coere d'Alene for the Grand Design rally in October, so maybe I can pick some brains up there.
 
Yes, my axles are Dexter, and it would appear that Dexter is the only site that says 3 amps is the max, but they also mentioned nothing about checking with a clamp on amp meter. All other sites having to do with trailer braking and trailers in general, cite 12" brakes as 4 amps or a bit more. Go figure.

I did have the truck running, and the gain maxed out on the brake controller. No, no voltage reading, no easy access to a bare wire for that. I'm plugged in to shore power, so low voltage really shouldn't be an issue. .

On my F350 the voltage drops when under around 10MPH to prevent overheating coils when stopped. With a foot on the brake pedal my voltage was 7-8v IIRC. I meant to check it with the manual switch to see if it also was reduced. When a get a few minutes I will check with the break-away switch pulled out since that should be the full 13.2v.
 
I ran a new wire from pin box back in my 399. I used 12 awg marine grade wire and ran it in a wire loom along the frame rail to the brakes. I also used the 12 awg wire to go between both sides of each axle.

Where did you run the wires from the pinbox? There does not seem to be a simple way to go from pinbox to the underbelly.
 
Where did you run the wires from the pinbox? There does not seem to be a simple way to go from pinbox to the underbelly.
I connected directly in the junction box where the 7 way plug ties into camper. I loosened the screws on the underside of the 5th wheel behind the pin box area and used fish tape to get the wire from pin box area to the front storage compartment. From there, I went through the bulkhead penetration where the hydrualic lines goto the curb side propane compartment and then down to the frame rail and followed it until I reached the brakes. I used wire loom and rubber lined wire clamps to attach to the frame. I opted not to go through the underbelly, I didn't see any benefit.
 
Okay, I'm a bit confused, not a new condition. :) You ran wire directly from the 7-pin junction box to each brake? Wouldn't that only provide the power from the pigtail from the truck? I thought the brakes were triggered by the 7-pin, but were actually fed power from the RV battery. I just didn't think the truck wiring could supply the necessary amperage to all the wheels. What am I missing?

On Edit. After doing some searching and reading, I see I was completely wrong about how the brakes are supplied electricity. It does come strictly from the tow vehicle. Now I wonder how the little wires in the pigtail are supplying 16 amps to my brakes. Live and learn.

Also thanks [MENTION=49842]DRedmond[/MENTION] for the suggestion about the truck not supplying full power under 10 mph. Even with 12 gauge wire from the junction box to the brakes, it's still only getting what amperage is possible from the pigtail. I wonder what the gauge of that wire would be.
 
Last edited:
Okay, I'm a bit confused, not a new condition. :) You ran wire directly from the 7-pin junction box to each brake? Wouldn't that only provide the power from the pigtail from the truck? I thought the brakes were triggered by the 7-pin, but were actually fed power from the RV battery. I just didn't think the truck wiring could supply the necessary amperage to all the wheels. What am I missing?

On Edit. After doing some searching and reading, I see I was completely wrong about how the brakes are supplied electricity. It does come strictly from the tow vehicle. Now I wonder how the little wires in the pigtail are supplying 16 amps to my brakes. Live and learn.

Also thanks [MENTION=49842]DRedmond[/MENTION] for the suggestion about the truck not supplying full power under 10 mph. Even with 12 gauge wire from the junction box to the brakes, it's still only getting what amperage is possible from the pigtail. I wonder what the gauge of that wire would be.

As I understand it, the truck supplies power to the brakes under normal driving, and of course that voltage is varied depending on the pressure on the brake pedal and the resultant output of the brake controller. The breakaway switch powers the brakes from the RV battery if/when it is needed during an unplanned disconnect from the truck......
 
Yessir, I think I finally got the whole thing. I just always thought it was like the break-away cable: the 7 pin cable just communicated to the trailer how much voltage needed to be applied to the brakes, and the trailer obliged, using the trailer battery. But everything comes from the truck via the brake controller and pig tail.

Thank you all, just shows to go ya: learn something new every day. Much obliged.
 
Update - Thanks for all your inputs, particularly @Hoopy that got me thinking. I had to quickly draw out the circuit to make sure I was looking at it correctly, I was. BUT, I had better check the brake trigger wire size from the junction box, it might be big enough already. The Blue Ford brake wire is 12ga to the truck 7-pin, 12ga from the male plug to the junction box, AND 12ga in the harness going into the RV.

I just need to find that wire in the generator compartment and connect my 4x14ga wires to the brakes and problem solved. I found where the junction box harness comes through the passenger side propane compartment then found it high in the generator compartment, just above the battery. I opened the harness and found a '"12/2 Jacketed Brake Cable" coming from the junction box and followed it down into the underbelly! No reason I cannot make my waterproof connections in the underbelly and run the 4 wires back.

What I thought could be a difficult fix turns out to be very easy. Not sure how much it will help but should take away some resistance and get the brake wires out of the axle tube.
 
Keep us updated on how it's going, please.

Pulled down the coroplast today and quickly found the brake cable coming from the generator compartment into the underbelly. Cut it, put a couple of WAGO connectors on and ran the 4-14ga cables back to the axles. Burnished the new brakes in and they are strong for magnetic. I didn't expect to see a significant difference but have done everything I know to do for the best magnetic brakes. Theoretically, I should have reduced the voltage drop by almost 1v. And, no more wires running through the axles.
 
So you have noticed a difference from before you rewired them?

Yes, but I suspect most of it was the new brakes. Original brakes had really not worn the drums so I don't think they were burnished in well. Got these babys smoking!
 

Try RV LIFE Pro Free for 7 Days

  • New Ad-Free experience on this RV LIFE Community.
  • Plan the best RV Safe travel with RV LIFE Trip Wizard.
  • Navigate with our RV Safe GPS mobile app.
  • and much more...
Try RV LIFE Pro Today
Back
Top Bottom