How hard is it to put a trailer wiring harness on?

Since the Prius isn't made to tow, it's doubtful you'll find a plug and play harness. You'd need to splice into the oem wiring.

SCH-I535

 

Hi Pioneer Steve,

Welcome to Prius Chat... I have to wire up some trailer lights in the next few weeks.... So I just did a little research and it looks like you can buy a modilite plug and modify it: Prius Trailer Wiring

But I use to build campervans and install car stereos and unless someone on here corrects me I have a less expensive, or warns me of the unexpected, my less time/money consuming solution Is as follows:

1) buy a standard plug(s) for whatever is most likely/easily to connected to a trailer
2) open access panel for the right rear tail light
3) use a test lite to identify which wire is night time running light, which wire is break light
4) tap into those two wires with blue wire splicers plugs: http://bit.ly/1hZdrvd
5) find a convenient place to screw a ground wire to the chassis
6) find a rubber plug on the underside of the vehicle to run the wires out of
7) make sure increased electric load of trailer lights doesn't screw up break lights
8) attach my trailer and wait for people too many people to help them move stuff

Not sure why they make such fancy trailer light kits that are more elaborate? I mean 40 bucks instead of $4? What's up? Maybe it's a waste of money, or maybe there's something I don't know?

Anyways, you can read about the more money spending solutions here: trailer wiring harness info for 2007 Pri | PriusChat

 

You wrote it yourself: the trailer lights increase the electric load, not only on the brake lights but also the taillights and on the flashers. Often most importantly the flashers, because the older ones would depend on having the right electric load to flash correctly, and the newer ones can be electronic and not tolerate overload well. The "more elaborate" converters have a wire you run to the 12V battery (really easy in a Prius because it's right there next to the taillight connections you're making anyway), and it only uses the car's own circuits as controls that tell it when to send power to the trailer set straight from the battery.

The other reason you didn't write yourself is that typical trailer light sets assume that brake and turn signals are combined: yellow and green go to the bright filaments on the two sides of the trailer, and the turn signals blink them individually, while the brakes just light them both together. But your Prius has a brake light circuit separate from the turn signals. In converting from that setup to a trailer set, you need a circuit that will power both yellow and green whenever the Prius brake circuit is on, but will not back-power the Prius brake lights when the turn signals flash, or one turn signal from the other. That's what's built into the "elaborate" adapter.

A Curt 56146 works well in the Gen 1. Not quite as easy as an adapter with matching T connectors you just plug in at the taillights - it just has six stripped wire ends that you attach to +12V battery (through a fuse), ground, left turn, right turn, brake, and tail. Coming out the other end it has the standard 4-pin flat trailer connector on several feet of wire, enough to lead out of the trunk and hook to the trailer.

-Chap

-Chap