Wacky Electric brakes

[Mrtoner]

So I tested the electric brakes by pulling the safety pin, and nothing happened - trailer still rolled. I figured since it is a 2001 that some things might need fixing. Started by looking at the brakes - magnets totally worn but everything else is ok. Ordered magnets.

Checked the circuit to the magnets and got no voltage, and I don’t see where there is a fuse or breaker for that circuit.

Checked the safety switch, and at first thought it was ok, but then my wife accidentally wiggled the pin in the “off” position and I got intermittent connection; found the same thing in the “on” position. Ordered new switch.

This is where it gets interesting. Diagram shows the blue wire going to the magnets. I checked and the magnets get the blue wire and ground, so I would assume the blue is POSITIVE.

BUT, the blue wire checks out as NEGATIVE.

The diagrams show a negative ground, and this is just a DC circuit, so for the magnets to work, the blue needs to be positive since the other wire of the magnets goes to ground.

Am I missing something?

Once my magnets come in I will test out at the battery with the new switch, and then reconnect the existing blue wire appropriately.

Does this all make sense?

 

[RichR]

Could the switch be wired backwards? But that seems rather hard to do with a single pole switch. Is the switch connected to the positive side of the battery? The brakes are definitely to be positive.

 

[Mrtoner]

Could the switch be wired backwards? But that seems rather hard to do with a single pole switch. Is the switch connected to the positive side of the battery? The brakes are definitely to be positive.

The switch had been replaced before, since the wires are spliced. A continuity check on the blue wire inside the battery compartment shows it is direct to negative.

Since the magnets are worn, the brakes worked at some time, but I think someone replaced the switch and somehow wired it incorrectly and moved things around.

I noticed on my Towlite that the magnets had one wire connected to a white ground wire screwed into the frame.

Anyone know if that is typical? From a reliability standpoint, screwing into the frame at such a high exposure location is asking for trouble from corrosion.

Just my thoughts.

 

[KnottyRig]

It’s common to use a floating ground like that on trailers. I hate it. Floating grounds are problematic enough in cars where everything is protected.

White (IIRC) is standard color for ground on trailers.

You can try to cleanup where the white wires ground (remove wire, grind the spot clean).

Push comes to shove, you can run a ground wire from the front of the trailer to each brake ground. I did this on a trailer cause I didn’t wanna deal with the problems of a float.

 

[marininn]

Brake ground?
Brakes that I have seen are not grounded and the magnets do not need to be hooked up special. Just a 12+ to one wire and a 12- to another wire. There is no ground.
Actually, for brakes, the voltage is 6 volts max. There should be 2 volts always to the magnets, this does not engage the brake, but when brakes are applied the voltage increases from 2 up to 6 depending on how you have your controller set. The breakaway should send the full 6.

The blue should be the brake wiring, this is 6volt+ that comes from the breakaway and/or the 7-pin plug from Tow Vehicle, TV.

Magnets usually have two black wires (as opposed to a black and a white). There is no set positive or negative on magnets, works either way. Just put positive to one wire and neg to the other.

Easiest way to work on brake electrical is to replace all the wiring. Quicker than finding the problem.

Get new magnets. These wear out just like the pads. Get pads if needed.

I ran two wires from the front (breakaway thing and trailer plug) to the side compartment. There are holes already in it. Inside the compartment you can access your wiring job without crawling under the trailer. I made 4 connections (or 8) for all 4 wheels. 4 positive and 4 negative. The negative can come from any ground or make your own from the frame or use the current ground.
I ran the 4 pair of wires to the 4 wheels.

Factory would daisy-chain the wires and split them off at each wheel, but wire is cheap and having 4 separate wires for individual brake magnets makes trouble shooting easier (and inside the side compartment), and keeps connections from being made under the trailer - which is in the elements.

Zip tie everything neat and above the frame and out of harms way. Zip ties are cheap too.