Rewiring trailer brakes, best place to ground them?

One wire is for 12 volt power to the brake magnets and the other wire should be grounded either to the trailer frame or to the main trailer ground wire. It does not matter which wire is used for power or ground because they are not polarized.





I prefer individual grounding vs junction box
Loose a ground and only one brake is affected vs ALL brakes

I ran one pair of wires per drum and led them all forward to a terminal strip. That makes any future problem diagnosis easier to accomplish.

You can ground the (-) phase of the brake wiring to any clean frame point. The size of the steel in the frame will preclude any large voltage drop from resistance in the circuit. If you do choose to ground each (-) brake wire, individually to the frame, you will have six (6) 12V frame ground points to maintain, four from the brakes, the battery's frame ground, and the ground from the towing connector umbilical.

westend wrote:
I ran one pair of wires per drum and led them all forward to a terminal strip. That makes any future problem diagnosis easier to accomplish.

You can ground the (-) phase of the brake wiring to any clean frame point. The size of the steel in the frame will preclude any large voltage drop from resistance in the circuit. If you do choose to ground each (-) brake wire, individually to the frame, you will have six (6) 12V frame ground points to maintain, four from the brakes, the battery's frame ground, and the ground from the towing connector umbilical.

I like this way. One location near the front of the trailer. Still have connections at all four drums, but the ground is in one place.

Thanks for the info!

Vintage465 wrote:
...One location near the front of the trailer. Still have connections at all four drums, but the ground is in one place.

Redundancy of multiple grounds insures the system operates when needed. With one ground, if it is lost, none of the brakes work at all.

I would think one ground per axle would be best, if you lose ground on one side but not the other you could have really weird turning behavior. With my trailer it's light enough that the truck can easily stop it even without the trailer brakes (before I started a written checklist I twice forgot to hook up the cable to the truck so I know it works fine even if it's not as safe) so I'd much rather lose the brakes altogether than have it pulling to one side.

Are you saying you are going to operate one axle? That is illegal and dangerous.

beemerphile1 wrote:

Vintage465 wrote:
...One location near the front of the trailer. Still have connections at all four drums, but the ground is in one place.

Redundancy of multiple grounds insures the system operates when needed. With one ground, if it is lost, none of the brakes work at all.

Maybe, maybe not. MO is that it is easier to maintain a couple good ground attachment points than a bunch of them. In fact, when I rewired my trailer, I even positioned the two main frame grounds (12V and 120V) next to each other on the frame. Then again, I trust my wiring skills. I have my brake wires led into conduit and then to a terminal strip inside a metal box on the tongue. Not many TT owners are going to go to that much trouble but anything to change the typical daisy chain to a star configuration is miles better, IMO.

Why do you think modern cars/trucks have duel chamber master cylinder...

loose one and still have one...


Smart.

also, do NOT depend on trailer hitch/ball/receiver to provide a ground between car/truck and trailer.... Wires Please.

When I rewired my brakes I ran a pair of 10 AWG wires from the pin box back to a busbar that I placed near the axles. From there I ran individual pairs to each drum.