Is there a good place to find a towing harness for lighting a trailer with the Fit or are they pretty universal?

Also, is there a place on the fit to plug the trailer harness into in the back or am I going to have to plug it into the harness up under the dash?

 

U-haul is your friend. Unless you don't live in the USA, in that case I can't help you.

 

or he could splice into the rear tail lights through the trunk access (corner panels in the trunk) and push through the grommet right next to it to access the bumper area. I would suggest a custom grommet that fits that, and fit the harness through that and tie it to the towing arm you will install.

 

Spend $45 on a real harness and don't hack up your wiring.

I have one of these waiting for it, me, and my Fit to occupy the same space and time. I've used similar harnesses before, and they're definitely the way to go. The harness connectors function as a pass-thru for the car's wiring harness, so once you gain access to the wiring, it's very simple to install.