Trailer wiring help

seachangeexcavation · Jan 30, 2019

First post!
Looking for some help on my tilt deck trailer that I use to pull around my holder A60 tractor I use for lot clearing.
Break away system was ripped off while digging the trailer out of the snow and now trying to re wire a new break away plug and battery box. Trailer is a load trail tilt deck with a 7 way plug that was not damaged. New break away system is two wires, new battery box is three wires. I know one of the break away cables goes

to the battery box 12v+, and the other goes to the electric brakes. Two remaining wires on the battery box with one a ground and one the 12v+ from the 7 way. Here’s where it gets screwy. Assuming my trailer harness is factory as it looks to be there should be two wires (I’m assuming ) for me to wire into as stated above (electric brake and 12v+ from 7 way). I have three wires coming back from underneath the trailer where the 7 way connects to the main harness. Two reds and a white. When I plug in the 7 way to my truck both reds are hot and the white needs to be grounded in order for the battery box to show it’s charging. To clarify the battery box has its own ground cable which I grounded but unless I ground the white wire coming out of the trailer the battery box does not show it’s charging. So if I’m to take it that the white wire under the trailer needs to be grounded that leaves two red hot wires. I get I could use one to be the hot lead going to the battery box but that leaves only a red hot wire for the electric brake connection. I’m stumped and called load trail who were no help. Any and all input appreciated!!

Industrial Toys · Jan 30, 2019

I have trouble following.

I am good at this stuff and notice people that are not often think wire color means something, when it often does not.

The break away is just a switch. It gets pulled and closes the circuit to the electric brakes from the on board battery. Battery + to electric brake circuit, through switch.

There is a common battery connection, negative.

There is a charging lead for the battery from the vehicle. I dont know if they employ any special charging circuitry, but I dont think it matters in this case.

Not often I see Holder mentioned. Almost bought one late last year.

seachangeexcavation · Jan 30, 2019

Thanks for chiming I’m, I tried to do my best to lay things out clearly but sometimes the harder I try the more confusing it gets. I follow what you said but one thing is still missing. Where is the wire for the electric breaks? Looking at my photos both red wires are 12v+ when i plug In the 7 way, so if I assume one is the source of 12v to the break away battery and the white wire is the ground that leaves only a already 12v+ hot wire as the electric break connection which can’t be as the whole point as you wrote is for 12v+ to be applied when the break away cord is removed.

Oh and I’ll make a post on the holder soon as it’s a funny little machine.

M5farms · Jan 30, 2019

Most trailers and pig tails use blue wire for brakes .

ruffdog · Jan 30, 2019

It looks like the power red and ground white (from truck) are used to charge the battery. When the switch is yanked free, 12v is sent from the battery to the brakes through the blue. The brakes should already have their own ground through the system.

Industrial Toys · Jan 30, 2019

The pictures really dont show where stuff is coming or going. You could easily get the 7 conductor plug wiring and use a multimeter to see which prong the brakes is. It is not impossible that the trailer brake circuit has power all the time as a monitor (very little current) so the vehicle (as on my GMC) knows that the trailer is attached.

George2615 · Jan 30, 2019

Here is the standard wiring for most trailers with a 7 pin plug. Not shown in the diag. is the breakaway switch. As mentioned, one wire goes from battery plus to switch and the other from switch to blue wire on trailer. The tow vehicle may not show power or brake voltage to the 7 pin unless connected to the trailer.

Trailer Wiring Diagrams | etrailer.com

ruffdog · Jan 30, 2019

Looking at some diagrams, it seems some break-away batteries were not wired with 3 wires so the truck would charge the battery. Some were wired with the ground and through the BA switch, pos goes to the brake wire.

seachangeexcavation · Feb 7, 2019

Sorry in my delay but finally got back to this project and appreciate the help.
I went with the theory mentioned here that maybe one of the two red wires was a low voltage hot providing feedback to the truck that it was connected to a trailer and doubled as the electric brakes wire. NOPE! Both reds had 12.3V when plugged in. After about giving up I laid on the ground to study the harness again and to my surprise noticed what looked like the very end of a wire sticking out of the harness junction. It was the blue electric brake wire! When the brake away cable got snagged and torn off it must of snapped the wire flush with the junction block. see attached picture
Thanks all for the help, trailers back in action.