Well, when I used to tow my buddy's boat (wired for his way, not standard) I just built an adapter. My flat 4 to his. Thats my suggestion. Buy a male and a female of the sizes/styles required and swith the wire around between the two so the right pin goes to the right socket. Then wrap the wires with different coloured electrical tape so it's easy to tell which is which. The cost will certainly be less than buying your own trailer .

 

I know, I know! The thread has gone cold. (My conscience has gotten the best of me) I paid a visit to my trailer builder today and asked about plugs on the trailer. One can specify any end he/she wants without regard to NHTSA or DOT as long as the side markers and taillights work. Turn signals don’t have too in some states!? One can specify 4, 5, 6, or 7 pin connectors to be installed by the trailer mfgr. Oops. Sorry.
GooseneckNat

 

At one time i found a diagram for wiring trailer plugs.

It had several classifications

4 pin round
4 pin flat

5 Pin round

6 pin commercial
6 pin RV

7 Pin RV
7 Pin commercial

Dont know if that helps I thought it was weird. it was out of the late 80's and some of the plugs like the 5 pin it even stated hadnt been used for quite a few years.

I think the 7 pin commercial was for tractor trailers and the plug had round pins insead of flat pins like an RV 7 pin.


My last couple of trailers were wired with either a 7 pin commercial with an adapter to 7 pin RV in a locked box or 6 pin wired in teh commercial fashion with an adpater in my box also. i do this so that if someone asks to use the trailer or tries to steal teh trailer who i dont want using it i forget to mention the adapter in the box and usually thieves get nervous when tehy have to start fiddling around with things or they unplug it and stand the chance of getting pulled over with no lights