I just installed my hitch and wiring harness yesterday. Just go to the dealer, pay the fifty bucks for the real wiring harness and relays. It took me all of 15 minutes to install and everything's all hunkey dorey, no messing around with voltmeters or wondering how it all works. It's all a simple plug and play install with good instructions. It's totally worth $50 in my book.

Having put a quarter million miles on a trailer rig myself and having had every problem known to man come up during that time, I can assure you that relay isolation between the tow vehicle and the trailer is worth every penny. Trailer wiring is notoriously crappy and some trailers draw quite a load on running lights. Doing it right is totally worth the time and energy. It's a heck of a lot better than having your trailer lights burn up the headlight switch in your vehicle and stranding you without lights in the middle of the night with someplace to be in the morning (not to mention the added trouble and expense of replacing a $100 switch now). Plus in the time you spent writing to the forum and researching how to get around using relays you could have installed them already.

Sorry to seem blunt, but I have a lot of experience with this stuff, and some things just aren't worth saving a penny over. This is one of them IMO. Good luck whatever you decide.