Trailer Brake Help, Please!!

[Squid]

Ok guys, hopefully somebody can help me out and end some serious frustration here.

One of the boats I fish on a lot is a 33' Palmetto Custom Center Console. I drive a GMC 2500HD that I tow the boat with. My truck only has the round type plug for the lights, etc., but I use the adapter to change it to the 5 pin flat plug since that is what is on the trailer.

The problem is that when I put my truck in reverse to back the boat down the ramp (or anywhere else), the trailer brakes engage and lock the trailer up. The brakes on the trailer are the surge type where they slide when brakes are applied on the truck. Lately I've been having to get out and wedge a 4x4 block of wood in the gap in order to prevent the brakes from engaging. This works fine, but is a major pain in the ass for me, especially at the ramp.

My question is, what can I do to figure out what/where the problem is? I've thought about checking the voltage on the plug to make sure that it's getting power to the relay on the trailer but cannot get any kind of voltage reading with the truck and lights on. (I assume that when my backup lights come on that it sends a signal to a relay that overrides the trailer brake system.) Everything else on the trailer works great...lights, turn signals, clearance markers.

Pictures of the whole system are below so hopefully that'll make it a little easier to understand. I know that it's either a wiring issue on my truck or the relay on the trailer that is causing the problem, but am clueless on how to check each one to diagnose the problem.

Any help will be greatly appreciated!

Bryan

[flndrpndr23]

There are two possible problems. The truck is not wired properly or you have a bad solenoid on your trailer.
To test for incorrect wiring you will need a 12v test light. With your round to 5 pin flat adapter plugged in to your bumper put your truck in reverse (with parking brake on !!) and you want to test for power from the outermost female socket on the connector. This should be connected to the reverse lights on the vehicle. If you have power here you then want to test the solenoid on the trailer.
Attach the trailer to the vehicle and make your trailer connections as you would if you were to pull the boat down the road. With everything connected put the vehicle in reverse (don't forget the parking brake). Go to the back of the vehicle and disconnect the trailer plug. While you do this listen very closely to the back up solenoid. As you quickly connect and disconnect the plug assembly you should here a click from the solenoid (providing you have power from the reverse light circuit). If you do not hear the click it may be the solenoid.
From past experience I have never seen a bad solenoid. It always seems to be the wiring.
Another thing to know. From the trailer it the "blue" wire that attach's to the solenoid. This may help with your trouble shooting.
It is also advisable to make sure you have a good ground between the vehicle and trailer.
A very inexpensive test tool is available at the auto parts store. It is a devise that plugs in the vehicle at the trailer connection and has individual test lights that tell you that all the connections are wired correctly.
Good luck.
Doug