I hate the little flat four plugs, they look like shit just hanging there. I like the round plugs and have always used the ones that competitive trailers use, U-haul also carries the same exact one. I mount one in the trailer too, make up a nice little pig tail and keep it in the car. I can't stand wires hanging from the trailer either. The female end of the plug has always fit very nicely in the same hole that houses one of the license plate lights on the last 3 trucks/suburban that we've had. I don't like drilling un-necessary holes in my boats, or cars.   

 
To each his own.

There is a definate advantage to having your tow vehicle equiped with the round 7, you'll always be able to tow any trailer you want to (electrically speaking).   

I definitely have to agree witht hat one!  I have the round 7 on my truck and bought an adapter at Pep Boys that has both the flat 4 and flat 5 on it.   Pretty sure I can tow just about any modern trailer with it now!

Rod - I have a few things I need to get done on the boat!  I had the engine replaced last year, came back without the bilge working, tac no loger works.  I probably need to get it all working once I get the bowl back on it so I can put it on the water.  The boat is stored in Riverside, i can bring it to you if that works better.  Not sure what it will take to get it all done so I am not even gonna ask you a price right now.  I'm heading out of town until May 6th, maybe sometime in May if you want to take a look at it?

Rod - I have a few things I need to get done on the boat!  I had the engine replaced last year, came back without the bilge working, tac no loger works.  I probably need to get it all working once I get the bowl back on it so I can put it on the water.  The boat is stored in Riverside, i can bring it to you if that works better.  Not sure what it will take to get it all done so I am not even gonna ask you a price right now.  I'm heading out of town until May 6th, maybe sometime in May if you want to take a look at it?

No problem, let me know when you're ready. Thanks.   

Most boat trailers are wired up one of two ways, either a pair of wires running down each side of the trailer or 3 wires running down one side, around the back, and half way back up the other side of the trailer. Typically Brown wire is used for tailights/side marker lights. I have also seen it where there's two wires running down each side, one red and one black wire, in that case black is tailights/side marker lights.

deer, i made this mistake, make sure that each light is grounded well then it will work check the grounding with mounting screws and or loop to trailer at each light. good luck