trailer side brake wiring diagram?

[munimula]

okay, i did this time. i removed the old hydraulic brake housing from the front of my 78 excella 500. with that, i hacked away at some of the wiring i though was of no use since the trailer has been retrofitted with electric brakes.

anyway, i chopped one or two wires too many. i don't get the green light on my controller in the tow vehicle anymore.

does i diagram exist anywhere for trailer side brake wiring to and from the fuse panel? that would be a huge help in getting this thing wired correctly.

i cut the ground from the neg post at the fuse panel. now i don't know what the cut end should attach to. i hope hooking that up properly will give me a closed circuit and a green light again.

i've been to tekonsha and dexters sites and could not find wiring diagrams at either.

it seems like the answer should be so simple but I can't get it!

thanks in advance,
dave

http://www.micsupply.com/airstream.htm

[nickcrowhurst]

Dave, http://www.airforums.com/forum...&threadid=5424 is a thread which contains some information on fixing butchered brake wiring. I will describe the system on my Excella, in the hope that yours is similar. My Airstream manual has diagrams which explain the wiring, but I'm 4000 miles from the trailer. Basically, the brakes operate when a 12 volt power supply connects to the wheel magnets by one blue wire in parallel to each wheel. Fortunately, for ease of maintenance, these wires do not go direct along the frame to the 7-way connector, but are routed up to the fuse panel behind the gaucho. There they are joined by the blue wire from the breakaway switch, as described in the thread 5424, giving the coach battery as a source of 12v in the event of an uncoupling. The blue wires from the magnets are linked at the fuse panel to the brake wire (blue?) from the 7-way connector. The other wires from the magnets, and the ground from the 7-way are all connected together at the ground post on the fuse panel behind the gaucho. The 2 wires from each magnet are interchangeable.I hope this helps. Nick.

[munimula]

as a follow-up. spent the day checking all connections at the wheels. cleaned up the wiring and made new splices to the hot and ground wires.

went back the the tow vehicle - still no light. i still had the dangling wire coming off the fuse panel ground side. i touched that to the hot wire going back to the brakes and the light at the controller lit up!

however, still no brakes. still looking for help on this. one would think a trailer side wiring diagram would be out there. i hit a few hundred links on google last night with no luck. you can be assured that once i figure out the logic of trailer side brake wiring I will post a wiring diagram.

i guess the thing that adds a hick-up to this is the break-away switch. AAARRRGGGHHHH!

[nickcrowhurst]

Dave, the breakaway switch is pretty much irrelevant. It is a parallel source of 12v power, so the wires to the breakaway switch can be disconnected by the switch, and you can fault trace the brake circuit independently. Another thread that fault finds the brake circuit is http://www.tompatterson.com/Airstrea.../msg00436.html
A wiring diagram is not going to be of much more help. You only have to test one wire coming from the tow vehicle, through the 9 way connector, up to the fuse box, dividing then in parallel to one wire per wheel magnet, and returning from each magnet to the ground at the fuse box. Test it out, starting at the tow vehicle, as in the above thread, and, using a digital voltmeter, you will trace the problem. When you have fixed it, you can re-connect the breakaway wires, and see if there is a fault there as well. (There was in mine.)Good luck.

[munimula]

nick,

thanks for hanging with me here. when i bought the trailer, the curb side brakes were working. i could see from visual inspection that the wiring on the street side had come apart. i have since made those connections in and around the brakes.

the wiring looks like this - one hot lead going from the 7-way plug back to the forward curb side wheel. from there, the wiring hops to the back wheel, the a hot and ground lead cut acrross to the street side wheels.

you are saying a ground lead need to come back to the fuse panel. makes total sense to me, however, the trailer brakes were functioning with grounds from the brakes to the frame of the trailer.

if i am to run a ground wire back to the fuse panel, should that come from the last wheel in the chain?

--dave

[nickcrowhurst]

Dave, it sounds to me as if the conversion to electric braking was done inefficiently. There are a couple of issues here:-
First is the issue of using the frame as the ground return. This is standard practice on automobiles, but when you have dissimilar metals in contact (aluminium skin and an iron-based steel frame on an Airstream), and spray them with an electrolyte (salt and other chemicals to prevent icy roads in the winter), you have a good set up for electrolytic corrosion. If you also make the frame part of an electrical circuit, things are just perfect. That's why my Land Rover Discovery corrodes wherever the aluminium skin touches the steel frame. I suspect some Airstreams use the frame as ground, but I also suspect they will suffer from leaks due to the aluminium crumbling to powder in places, especially near rivets. A non-conducting gasket, or zinc chromate paste, between the two metals does help, but the fastenings are still a problem. In short, I wouldn't use the frame as ground on my trailer. It's often done just because it's easy.
A second issue is the layout of the wiring. If the brakes are ever to balance, each of the 4 parallel circuits should have the same electrical resistance (and therefore the same length of the same diameter wire), so the same current flows through each magnet. I would disconnect all the existing wiring to the wheel magnets, and discard it. I would then go to the point on the fuse box where the brake wire from the 9-way connector is attached. From the other side of this fuse I would attach 4 blue insulated wires of equal length (about 20 foot, of the size specified in the Dexter website, or thicker). These can be taped together, and run down through the floor and along the bottom, or inside the curved edge of the bottom, through conduit to near the axles. One wire now goes to each magnet, tucked away or again in conduit. (It doesn't matter which wire on the magnet). Do the wheel furthest away first, and then cut the other 3 wires to the same length. Now connect the other 3 wires, and coil away any spare wire in the conduiting. Connect another 4 similar gauge 20 foot lengths of wire (a different color, perhaps white) to the other wire coming from the magnets. Tape these together, and run them in another piece of conduit, and up through the floor, to the ground post on the fuse box behind the gaucho. Once that is all working and tested, the breakaway circuit can be added. Take a 12 volt battery supply from the + side of the fuse box, using a blue wire of the same gauge as the brake wire through the 9-way, and route this through the A-frame to one wire at the breakaway switch. Now connect another wire of a different color to the other wire from the breakaway switch, and lead this back to the post in the fuse box where the brake wire from the 9-way is attached. The important thing about the breakawy switch is that it is "normally open". Unlike most switches, this circuit is COMPLETED when the pin is pulled out, not broken. It simply provides a 12 volt battery supply to enable the brakes when the trailer breaks away from the tow vehicle.

It will take a day or two of work, but at least you will know it's safe. If the existing live wire from the fuse box to the first wheel is of sufficient gauge, you may be able to use this, and split into the 4 equal wires from near the axles, saving some work, but I wouldn't recommend it, as the joints would be hidden under the trailer. I don't claim to be particularly knowledgeable about these matters, but I can pass on my practical experiences. Good luck. Nick