I just bought a used tandem axle boat trailer with surge drum brakes and a 5-pin flat harness. I understand that the blue wire in this case is used to disengage the brake system when backing up.

I had to make a 7-pin to 5-pin pigtail connector to plug it into my 1997 F350. Other than having to switch the left and right turn signal wires in the plug, it worked fine and all the light functions worked great.

I plugged the blue wire into the center terminal on the 7-pin connector. When I was bringing the trailer home this morning, I was getting a voltage reading on my Prodigy brake control, and an intermittent "S.H." code flashing, which appears to be some sort of a short circuit code? Turn signals, brakes, and marker lights were all bright and working fine- the dealer just replaced them with LED's.

I don't understand why my brake control s any sort of a reading at all pulling a trailer with surge brakes. My last boat trailer only had a 4-pin, and the controller never even registered a connection.

I only pulled the trailer empty and didn't have any problem backing up, but don't want to have any issues backing an 8,000lb load down the boat ramp.

I really hope there's a simple answer....

 

Look at this: Trailer Wiring Diagrams | etrailer.com

 

I think I may have found the issue today. I found that the blue wire off the trailer connector wasn't connected to anything and had a bare end. I put a piece of shrink wrap over it. Hoping that's where my short was coming from.

I took a multi-meter to my truck's connector and verified that the center pin was only sending voltage in reverse, as it should be.

I found that it's typically only surge DISC brakes that use solenoids (blue wire), whereas mine is a drum brake system.

 

I don't understand why the Prodigy was seeing the connection if the wire in question was hooked to the center (reverse lamp) pin.

 

I was wondering the same thing! I checked the center pin though, and it only showed voltage only when in reverse. I'm hoping the short had something to do with it?? I'm pulling my boat home on Monday, so we'll see.

 

That ones STILL got me scratching my head. I can't see how a short in that blue wire would have done anything other than blow a reverse light fuse, and I don't think you said it even did that. If you don't find an obvious answer, I'd look into the back of the plug on the truck. Maybe its got a frayed wire or something. The primary reason I've taken such an interest in your issue is that I've wired dozens (and dozens-literally) of trailers and trucks and cant come up with a plausible explanation for what your seeing. I'm quite familiar with the Prodigy, its my favorite aftermarket controller, and SH means short - as I'm sure you know. I just cant figger' where its coming from! As far as the reverse dump feature, my last boat trailer had drum brakes and had a standard 4-wire plug with no dump feature. The only time it was a problem was when backing up an incline. The brakes would actuate and you had to get out and manually operate the lock-out. Backing up on flat ground was never a problem, as long as you didn't jump on the throttle too quickly. Of course, once the boat breakes over the ramp its a non-issue. My current boat has surge/disc and is equipped with the dump valve. I guess discs actuate at a lower pressure.

 

Well I was still having the same issue today with my homemade harness, so I decided to try a Reese 7-5 factory adapter. Fixed the problem. My Prodigy doesnt even recognize a connection...which it shouldn't. I don't know where I went wrong in my pigtail, but oh well....works fine now!

 

Only prob is you are human. We all screw up - sometime. Congrats on finding your problem.