can a 4 prong trailer harness run electric brakes?

willys53allis · Apr 26, 2013

Got a buddy with a dual axle trailer with electric brakes. The trailer has a 4 prong harness, and the truck has a brake controler. Everything I"ve looked at says you need a 6 prong harness. Why if it needs 6 wires does the trailer only have 4?
Also he"s using an adapter 6 prong plug on the truck to a 4 prong on the trailer.

Leroy · Apr 26, 2013

If he is doinf that then it is because he doesn't have lights on the trailer. With lights they take up the 3 hot spots and the one ground spot so he is going without lights to have enough wires to feed the brakes.

mattwillson · Apr 26, 2013

Nope. Buy a heavy guage 2 wire plug and wire your brakes in thata way.

willys53allis · Apr 26, 2013

It's just the opposite, lights but no electric brakes .

old · Apr 26, 2013

It can be done but not correct. You need the brown wire for the running lights. The yellow and the green for the turn signals/brake lights and then it should have the last one as ground but some I have seen use the ball/hitch as a ground and then the last wire for the brakes but the problem is that the ball/hitch at best are an iffy ground and if he got in to an accident and they started to look things over he could be up a creek

John T · Apr 26, 2013

The more normal typical connection for 4 poles is:

1) Green Right Turn & Stop
2) Yellow Left Turn & Stop
3) Brown Tail/Marker
4) Ground

If the wants to use the hitch ball itslef to make up the ground to ground connection I DO NOTTTTTTT RECOMMEND THAT METHOD I guess he could use the No 4 for brake circuit BADDDDDDDDDD

The more normal typical connection for the 6 pole called Horse Trailer plug is:

1) Right Turn & Stop
2) Left Turn & Stop
3) Tail/Marker
4) Ground
5) Auxiliary 12 VDC Power (like for a bunk light etc or to charge a trailer battery)
6) BRAKES

The 7 Pole RV plug has yet one more pole for back up lights

Now which method is he gonna use??????

John T

willys53allis · Apr 26, 2013

It's just weird how it's 4 prong and has electric brakes and he said they've (brakes) worked before. But as "old" said it can be done, although it's not recommended. It's already wired like that and I was just trying to help him get the brakes working. Thanks for all the input.

John T · Apr 26, 2013

Youre welcome, yep as I noted if he has stop and turn and tail lights that takes up 3 of the 4 poles so the 4th normal ground pole he must be using for brakes and relies on the hitch ball to make frame ground connection with the trailer. Again that can work but like I said I do not recommend it lol

John T

David G · Apr 26, 2013

It has to be a custom wiring job, could be a bad deal if anyone else hooks up.

Really dumb to do things like this, just put the correct connectors on.

T in NE · Apr 26, 2013

The brakes could have been wired off a brake light. Not the best set-up, when you brake, the trailer brakes (at full power), but when you signal, watch out!
You could replace the 4 flat with a 5 flat, not the greatest, but it would be better than trying to ground through the hitch for a 4-way.

Leroy · Apr 27, 2013

If he is using brakes on a 4 wire then he cannot have lights but they are made for the lights and not brakes. Brakes only would work with a 2 pole coupler, think you might have missunderstood what I was trying to say.

t1 · Apr 27, 2013

He could have lights, sort of lol.

If you run your brake controller through the 4 way plug, to power the brakes, then splice your trailer brake light wires to the electric brake wires, you still get brake lights when the electric brakes are applied. maybe not as bright as you or I would want them however. and its certainly NOT the way I would do it.

Now, turn signals, thats something else. many vehicles flash the brake light bulb, so if not wired right, you could end up pulsing your brakes too. That assumes of course, that turn signals are even used. so many people today have no idea what that lever on the side of the steering column is for...

504-1 · Apr 27, 2013

Even if you wired brakes through a 4 pin,they are not heavy enough to carry the electric load for very long. Re wire the trailer and do it right.

W_B · May 2, 2013

(quoted from post at 19:29:22 04/27/13) Even if you wired brakes through a 4 pin,they are not heavy enough to carry the electric load for very long. Re wire the trailer and do it right.

Agree. Not that hard, even a dummy like me can figure it out. I wired one for a friend in the parking lot of a Tractor Supply in an emergency situation.

W_B · May 2, 2013

Darn double post!

W_B · May 2, 2013

(quoted from post at 19:29:22 04/27/13) Even if you wired brakes through a 4 pin,they are not heavy enough to carry the electric load for very long. Re wire the trailer and do it right.

Agree. Not that hard, even a dummy like me can figure it out. I wired one for a friend in the parking lot of a Tractor Supply in an emergency situation (regular tow vehicle broke down and substituted the pick up truck).

sflem849 · May 2, 2013

No way. Your buddy is a tool. I would put money that they never worked before. In order to work the trailer AND the truck would have to be rigged up to work properly. Then to do it through a 6/7 to 4 adapter.

BTW, to ensure I win the money I would hook it to my truck because I know everything works just fine on that.

can a 4 prong trailer harness run electric brakes?

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