5 - pin trailer wiring harness

[lawdog]

Buddy of mine just bought a boat with a five pin flat trailer wiring harness. The trailer is equipped with electric surge brakes. As with most every vehicle in the world, his Ford F-150 is ready for a 4 pin flat or a 7 round. I was thinking rewiring the five into a 7 round end would be the easiest fix to this rather than screwing with his vehicle and then having it to do all over again when he trades or if someone else pulls that boat.

Now my question, I know the first four wires will be standard hookup, but I'm thinking that surge brake can't go in the #2 blue brake pin as that is meant for electronic controllers. I've heard they are sometimes rigged to the auxilary pin #7 as that's for back up lights, but I don't know if that's how his truck is rigged or if they all are that way or what...

Any thoughts???

Thanks guys.

[Shorelunch]

They make 7 round to 5 pin flat conversion harnesses if that helps any. Most auto dealers have them.

[Eric Wettschreck]

Go to Runnings dude and get a 7 to 5 adaptor. I just bought another one (I keep losing them) and they are like 13 bucks.

[walleye_dog]

Yeah, the 7 round to 5 flat adapter is the way to go. The surge brakes are 5 flat because the fifth pin actually goes to reverse lights which trips a bypass switch for the actuator on the tounge.

[lawdog]

"keep losing them"...

I know this boat owner, and that's exactly why I thought I'd be better off hard wiring a 7 round end on there. He'll NEVER have that thing when its needed...

Any idea as to where I'd have to stick that fifth wire to make a 7 round end work???

[Jeremy airjer W]

This will help

[lawdog]

Thanks Airjer. I've seen those before, I just wasn't sure if that accessory was the place for the back-up light but looks like it is according to how its labeled in your diagram. I've always just seen it marked accessory so this helps confirm it for me.

I'm not really understanding this wiring for the surge brake, why would putting power to that wire (by turning on the back up lights) turn OFF the surge brake? Seems backwards to me... Guess its not really an electric brake at all is it???

[Macgyver55]

The surge brakes really are "surge" brakes. The additional wire is tapped into the backup lights to disengage the trailer's brakes when the vehicle is reversing, although not all surge brake equipped trailers have this option.

[John Mickish]

A trailer with surge brakes is very hard to back up without the lockout feature. Think about the physics involved for a minute and the lockout makes perfect sense.

[lawdog]

I get that part for sure, I was just thinking if the brake is electric then turning it on when backing up wouldn't work. Wasn't thinking that the only electronic part is the lockout of the surge brake, not the brake itself...