Re: (Another) Trailer Wiring Question
Not quite. The blue terminal is for electric trailer brakes on a typical 5 wire. A 7 pin connection for a reverse solenoid is from the center pin of the connector for the reverse lights, coded green. Tie Down reverse solenoids use a blue wire from the solenoid (another statement of the quality of Tie Down) but it technically should be green. The original poster needs to clarify his brake system to make the correct call. The blue wire on a 7 pin is connected to a brake controller for electric brakes if so equipped, and not common to most boat trailers.
Well, after looking at all the various instructions for wiring trailers I have come to the conclusion that there are numerous ways to connect the wires by color, but only one correct way by function.
It seems that there are some sites that agreed with me that the 5th, blue, wire is attached to the backup lights on the vehicle, while others indicate it is for the electric brakes. Some indicate the 5th wire on the flat plug is red although I have never seen it that way. (I suspect this is more a matter of semantics as in either case the wire is "hot" only when the brake pedal is depressed.)
Also, some 7 wire connectors reverse the center pin and "S" pins function.
Apparently there is no absolutes when it comes to the wiring, even vehicle manufacturers use different colors for the functions, even changing them over the years.
The best advise, I have concluded, is to verify the function of the individual wires at the tow vehicle's connector with a meter or test light, then make the appropriate connection based on your findings. Use the trailer plug wiring color code to attach to the correct color wire coming off the tailer lights, which I think use the same code universally.
I would suggest (this is what I would do in your situation), that you remove all of the old wiring up to the lights and begin fresh. You will find it much easier than trying to second guess the previous owner, and you will have fresh wires for your system.