Electric brake magnet wiring

[Jim K in PA]

I am installing the electric brake kit I got for my PUP via eBay.  The kit was relatively complete, and at a very good price.  However, there are no instructions.  My presumption is that the two green wires of the dipole magnet do not care which is hot and which is ground?

[austinado16]

I believe that is correct.

[wavery]

I think that I would test them. I think that they may both be hot wires. The magnets should ground through the frame. The second green wire may be intended to tie into the magnet on the other wheel.

I could be all wet on this, that's why I say, "Test them". It would be as simple as hooking up one of the green wires and putting a test light on the other (with the magnet grounded). If the test light lights, it is not a ground wire, it's intended to tie into the other brake.

I think that they may do that so if one brake fails, they both fail. If you run a hot wire to each side, you could have a failure on one side and the other side still working. That wouldn't be good.

[austinado16]

Just took a look at the magnet from my '83.  2 wires go to it, and it doesn't have a good way to ground itself because it mounts loosely on a metal shaft with a spring.

So.....I think it's power goes in, grounded on the otherside, and the magnetic field is then created.

Try it on your car battery and see if the magnet will stick to the inner fender or radiator support.

[AustinBoston]

I had to do a fair amount of digging to be sure (Dexter documentation is notoriously bad), but one wire is hot and one is ground.  It does not matter which wire is connected to hot and which to ground.

It boils down to this - the brake manufactirer does not know how the product will be installed, so they provide a lead for each side of the circuit.  It could be put on an all-wood trailer, for example, and then the axle would not be grounded unless the manufacturer deliberately did so -- an assumption that is highly prone to failure.

In addition, the magnets are mounted through a moving connection on a moving armature - another potential trouble spot.

If you want to be sure, check with an ohm meter.  The resistance for a single magnet for 7" brakes should be about 4.8 ohms, for 10" brakes about 4 ohms.  If you read this between the leads, then one is ground and one is hot (in this case, a reading from either lead and any other metal part of the magnet will be infinite).  

If you read 4 or 4.8 ohms between the mounting point and either lead, then ground is through the chassis (and the reading between the leads will be zero).

Austin

[brainpause]

As has been said above, one is hot, one is ground, but it doesn't matter. I added brakes to my ATV trailer, and this made life easier.

Larry

[Jim K in PA]

Thanks for the replies, everyone.  I hope to have everything wired and functional this weekend.