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Old 04-20-2005, 09:53 PM   #1
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brake wire questions

I am rebuilding a '66 soveriegn. I want to run new brake wires. I just put on new Dexter 12" plates with new brakes. I also plan to install a brakeaway switch. questions are,
what guage wire do I run to the brakes?
do these wires usually run through the frame from the tongue straight to the axels? How would I run new ones without pulling apart the floor or belly?
Any words of wisdom regarding hooking up the brakes and the brakeaway switch?

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Old 04-20-2005, 10:43 PM   #2
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Brake wire

Jon, I just got the floor out of mine (doing a complete rebuild). The brake wire looks to be about #16 (?). In mine, it begins at the 7-way plug, runs under the floor to above the tandems and goes through the belly pan down to the wheels. The breakaway wire runs from the breakaway plug on the jack, thru the frame from there, under the floor and up to the 7-way. If you can wait until tomorrow, I can try and take a few pics.

As far as how to run the new wire....hummmm. I'm affraid it's too late right now to be too creative, but one solution might be to use the old wire as a "pull wire" for the new. This, of course, assumes that the old wire is still in place. There are a couple of problems with that, however. In my '73, there are 4 seperate wires (one for each wheel) that split off the feed coming from the 7-way. I believe there are two feeds running aft to the split from the 7-way. I'm not near the TT right now, so I'm doing this from my poor memory. I'll have a look-see tomorrow and maybe give a more competent answer.


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Old 04-21-2005, 02:13 PM   #3
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Originally Posted by hickam
what guage wire do I run to the brakes?
On the ´78 sovereign (dual axel) 12gauge was original, and, I think, 12 guage is also installed on the MoHo to the tag axle brakes (electric), but it may be 14 gauge.

For the price difference, I would not even think about running anything smaller than 12 gauge.

There was another thread here recently that discussed (debated?) the pros and cons of fuses in the various circuits involved in the brake system.

The factory set up on the '78 was a single 50 amp fuse shared circuit to the electric jack and break-away switch....remember, when activated, the emergency (break-away) switch is going to throw a full 12 volts to the brake magnets - this will draw a lot of current (and create a lot of heat SOMEWHERE - either in the lines or the magnets themselves). The ¨normal¨ activation of the brake controller would probably present around 6 volts to the brake magnets. With a 50 amp fuse protecting the battery, I would think that a brake magnet would open circuit prior to the 50 amp fuse. Battery life would be VERY short should the break-away switch be accidently closed.

Also, on the ´78 Sovereign, the wires are partially in the belly pan and partially in the frame - I would think it would be a personal preference as to how you would run them.....half inch metal electrical conduit on the exterior of the belly pan would hide and protect the wires.

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Old 04-21-2005, 09:49 PM   #4
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Originally Posted by Jim & Susan
In my '73, there are 4 seperate wires (one for each wheel) that split off the feed coming from the 7-way. I believe there are two feeds running aft to the split from the 7-way.
I am still confused about how these hook up. I have two wires coming from each of the wheels. I was thinking that I would just ground one on the frame and pigtail the four other ones together and hook them up to the brake feed in the 7 way. Is there any reason to run each of the brakewires back to the 7-way individually? Can I use the chasis ground? Do I have to worry about which of the two wires that comes out of each wheel go to the lead versus the ground? Thanks for the help...
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Old 04-21-2005, 10:14 PM   #5
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The two wires coming from each magnet do not have polarity, either one can be positive or ground.

You should run the ground wire all the way back to the tow vehicle, through the 7-way plug. You can pigtail the grounds together to one 12 ga wire.

You pigtail all four magnets together (parallel), not in series.

I don't know the logic for running the ground all the way back, just that's what the manufacturer recommends for reliable operation.

You can get some information from this web site, about 3/4 of the way down the page.
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Old 04-24-2005, 01:37 AM   #6
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Hi, I found your questions interesting so I just went check my 1970 Overlander. I checked the current in the brake wiring when pulling the breakaway plug out. The results were 10 amps @ 12.7 volts. This means a maximum power dissipation of 127 watts assuming all 4 magnets were energized that means 127watts/4=32watts per wheel. As you can see it’s not very much. As far as the wire size, I feel like a minimum of 14 gage is adequate. Naturally, bigger is better and I would make sure to solder every connections after making a solid mechanical joint. Make sure to use stranded wire versus solid.

As to the reason for not using the chassis for return is because any connection made to the frame would be mechanical with dissimilar material (steel and copper) and would present a galvanic problem making a high resistance connection over time. Believe me the engineer who designed the system new what he was doing. Now my question is why do you feel like changing the wires?

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Old 05-01-2005, 09:19 PM   #7
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Thanks for all the good advice. I found some wire specially designed for electric brakes at a local trailer supply store. It has a sheathing that allows for it to be run outside. I am going to use this attached to the belly with plastic wire clamps. For the ground I will run it to the plug and attach it to the frame just to make sure. I'll let you know how it works.

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