Trailer brake question.

HawkinsHollow · Jun 4, 2019

Evening gentlemen,
I just bought an 85 F250, this truck has a trailer brake box under the dash. I am in the process of redoing an 18' car hauler to pull my tractor, I want to rewire the trailer brakes on the tractor to use them with my truck. Here is my question: I have noticed most trucks with trailer brakes have a 6 or 7 pin lights/brake plug on the back of them. This truck seems to have 2 four pin connectors on the back of it. I have done some preliminary research on this and I have seen nowhere that shows this sort of setup for trailer lights/brakes. Is this semi-common or am I missing something? One of the 4 pins is your average 4 pin you would see used for trailer lights. The other one is similar but a little different, it would NOT plug into your normal trailer light plug. Any help would be greatly appreciated. If pictures would help I will snap one tomorrow.

4570Man · Jun 4, 2019

4 pin trailer plugs are not brake equipped. Someone has wired that setup custom to their truck and trailer. They probably have one plug for brakes and the second plug for lights. That or the first plug stopped working so they wired a second plug without removing the first. It would be best to re wire the truck and trailer to the standard 7 pin setup. If you’re lucky the wires are still good. You’ll also need 12 gauge wire for the brakes not the dinky wire used for trailer lights. Good luck, I hate vehicles and trailer wiring. I’d also recommend a new brake box. They’ve come a long way since the 80s.

1010 · Jun 4, 2019

Go to truck accessory place and get a new every thing, being an older truck might be a minute to get hooked up but there is some pretty painless plug and play wiring..

Even the trailer brakes are just complete bolt on simple install..

jaxs · Jun 5, 2019

All the trailers with brakes around here have 7 pin plugs,that's what you should use for re-wireing truck. The only way of answering your questions about those 4 pin connectors is using a multimeter and/or test light. First,draw a sketch of both 4 pins including wire colors. Start by turning truck parking lights on and testing all 8 pins for 12 volts. Label pin(s) with 12 v as tail-running. Turn parking lights off and repeat with turn signals,brake lights and brake controller. Once all pins and wires are labeled on sketch,use this to wire 7 way http:///www.bing.com/images/search?view=detailV2&id=99F6DDDDDEB5DC322F936CD91BA19F3F1CE40645&thid=OIP.Cmz3LrXIOHQ4fUEcmhEuqAHaDt

Fallon · Jun 5, 2019

I concur. Get new everything & go with a proper 7 pin setup. If there are 2 4 pin connectors, either 1 failed or they did something really janky like wiring one up for brakes. Either way things arent right.

HawkinsHollow · Jun 6, 2019

jaxs said:
All the trailers with brakes around here have 7 pin plugs,that's what you should use for re-wireing truck. The only way of answering your questions about those 4 pin connectors is using a multimeter and/or test light. First,draw a sketch of both 4 pins including wire colors. Start by turning truck parking lights on and testing all 8 pins for 12 volts. Label pin(s) with 12 v as tail-running. Turn parking lights off and repeat with turn signals,brake lights and brake controller. Once all pins and wires are labeled on sketch,use this to wire 7 way http:///www.bing.com/images/search?view=detailV2&id=99F6DDDDDEB5DC322F936CD91BA19F3F1CE40645&thid=OIP.Cmz3LrXIOHQ4fUEcmhEuqAHaDt

THANKS for this reply and link, EXACTLY what I needed. Thanks for the rest of the replies as well.

LouNY · Jun 6, 2019

Most everything for the general public has transitioned to the 7 way flats,
that said there are still lots of applications with 6 or 7 pin rounds and some different configurations.
this page has many of them it does not show the two different configurations for the 6 and 7 pin rounds.

Fallon · Jun 6, 2019

LouNY said:
Most everything for the general public has transitioned to the 7 way flats,
that said there are still lots of applications with 6 or 7 pin rounds and some different configurations.
this page has many of them it does not show the two different configurations for the 6 and 7 pin rounds.
View attachment 607923

If you mess with the wiring at all on a trailer or tug, convert it to the 7 pin flat RV style. Maybe a 4 pin for a small trailer. It's easy to get an adapter for 7 pin & more compatible with everything in the long run.

I converted my old used 14k tilting deck from a 6 pin to 7 pin as soon as I got it. When I inherited a 1k 13' Boler RV trailer I converted it from 4 pin to 7 pin. It never had brakes, but 12v constant power was nice & it was more standard.