I am going to go out on a limb and say that the dude at the oil change place is at the oil change place for a reason. He's not a trailer repairman.
You say your boat trailer brakes aren't working. Is this statement based on your truck not recognizing the trailer? If so, your logic is incorrect because you do not understand how your trailer brakes work. Your truck is looking for electric brakes, which your trailer does not have. So, the truck is correct that it doesn't see any brakes - and it isn't expected to for your boat. Hence my comment about the dude at the oil change place.
I have never seen a boat trailer that mandated a 7 wire connector in order for boat trailer brakes to work. Your 5 pin flat connector is adequate as long as you have it wired correctly.
Though there have been some experimental electric brake boat trailers, they are extremely rare. The vast majority are mechanical surge-brakes. No electrical connection from the vehicle is required for mechanical surge trailer brakes to work. (More detail later.) You press the brake in your truck, the trailer rolling behind then pushes into your slowing-down truck. That push compresses the movable tongue that actuates a master cylinder inside the trailer tongue, thereby applying brakes to your trailer until it is no longer pushing against your vehicle. This balances the forward motion.
Google surge brakes to read about it. It would be a good idea to understand what you are towing down the road and the basics of how it works so that you can maintain the trailer properly and be safe.
I mentioned earlier that no electrical connection is required to make the brakes work - but there is that blue wire? Well, that wire has nothing to do with making the brakes WORK - it has only to do with making them NOT work when you want to back up. Trailers built with disc brakes have very good brakes. Backing up does the same thing as you applying the brakes when traveling in forward. You push back, so the brakes lock up. They can bind so tightly that things get broken! The blue wire has 12V on it when you put the truck in reverse. That 12V engages a solenoid that blocks brake fluid pressure from reaching the disc brakes, and this allows the special case of disabled surge brakes when the vehicle is in reverse.
Edited by Flippin-Out (02/06/16 08:12 PM)