Breakaway Switch Confusion.

opnspaces wrote:

Gdetrailer wrote:


Heck even on my TT, I have added a relay so when the pin is pulled it automatically disconnects the brake wiring electrically from the vehicle. The vehicle brake controller will now give you a warning of no connection before you start driving..

Gdetrailer, maybe I just haven't had enough caffeine, but having trouble picturing the wiring of your relay.

I can see a normally closed relay where the the brake signal wire runs through from the tow vehicle. But what are you using for the power and ground on the trigger wire?

Addition of a single pole double throw (SPDT) relay makes this happen, I used a "Bosch" style 40A relay.

Brake coils are connected to the common terminal of the relay, Brake wire from tow vehicle is connected to the NC Normally Closed) terminal of relay.

12V+ goes into one side of the relay coil, other side of relay coil goes to breakaway switch. Other side of breakaway switch goes to ground.

Pull pin, the switch now grounds the negative side of the relay coil, pulling the NO contact to closed position, this now breaks the NC terminal to open which the break controller now sees as no brake connection and alerts you. This same action now applies full battery voltage directly to the brake magnet coils.

You also get a few benefits, the breakway switch no longer must carry the high amperage and the relay coil limits the max current through the switch and any shorts will not burn your camper to the ground.

I did a drawing years ago but in reviewing it, I show a fuse on the relay coil, I don't remember putting one there but the power source is most likely fused or breakered, typically the breakaway system is not fused, but I suspect I used something like 30A or 40A just so the wiring is somewhat protected from major shorts (catastrophic fuse). I would have to take a look at my fuse block to see what I did.