How to Install Trailer Hitch Wiring
2004-2009 Toyota Prius
If you have a trailer hitch and want to tow a small trailer you're going to need lighting to be legal and this is easiest way to get there. Basically this product connects inbetween a factory wiring harness and is plug 'n play with no splicing required, you just make the connections - simple. All the cable lengths are sufficient out of the box. Some of the photos in the tutorial were taken at odd phases, be sure to follow my text for proper order of steps.
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- Thin flat-head screwdriver
- Socket wrench set w/10mm socket
- Cutter to trim zip-ties
- Tow Ready 118505
- Optional: extra zip-ties
The Tow Ready 118505 is basically 2 T-tap connectors that lead to a control module, from this you have positive and negative connections to the battery and your trailer wiring hook up. I wish I got a shot of the wiring spread out but forgot to as I wanted to get this in. Unfortunately I didn't buy this on Amazon and spent $40 more on it than I needed too....
Bundle of wires, 3 zip-ties and 1 grounding screw that's not needed.
1) Remove the rear cargo covers, steps 1-6.
2) Pull up on this tab and remove the driver's side light cover.
3) Pull up on this tab and remove the passenger side light cover.
4) Remove the driver's side 10mm tie down bolt and hook.
5) Stick a thin flat-head screwdriver in the left side of the wiring harness indicated by the blue arrow and pull to release the harness. The harness is held in place by a loose clip, you can just pull the entire harness out to make this easier. Just don't push too hard with the screwdriver, you don't want to break the plastic tab that locks it in place. Now untie the hitch wiring. Run the brown and yellow side across the back of the trunk, under the trim and above the tow eye location and out as shown.
6) Clip the hitch wiring in place. See how it taps inbetween the OEM wiring like a T. Tuck the wiring in behind the panel and reattach the light cover. The blue arrow shows the hitch wiring resting on top of the cargo eye location. Reinstall the cargo eye while holding the wiring up so it doesn't get pinched. Once that's in place the wiring should still be movable.
7) Zip tie the brown/yellow wire along this wiring in the rear of the trunk. They give you 3 zip ties but I used a few more.
8) Now repeat steps 5-6 to clip in the green and red hitch wiring into the OEM harness on the passenger side. This side has the control module which has a piece of double sided tape on the back of it. There's a perfectly sized flat area to mount it up by the blue arrow. As you can see, there's plenty of length to reach the battery and ground point and as you'll see, plenty of hitch wiring length as well. Unlike the drivers side I ran the wiring under the cargo eye so I really didn't need to remove that on this side.
This just shows the hitch module a bit clearer. I chose to have the hitch wiring coming down for added length and the side with all the lighting and power connections on the top. It would probably work either way. There may be other mounting locations but this is just what I saw that worked so I went with it.
9) Before doing this step you may want to hook up a battery charger or aux 12v battery to the jump posts in the engine bay so you don't lose all your radio settings etc. If you don't mind redoing all that proceed. This is where my photos will look funny because I messed up the order and didn't redo the photos. Anyway, loosen the 10mm negative bolt and disconnect the negative clamp from the battery, circled in red. Leave it disconnected and then unscrew the vehicle ground highlighted in green, add the white ground point for the hitch wiring and tigthen the 10mm vehicle ground - do not reattach the ground to the battery as the picture shows. Instead undo the 3 tabs and remove the positive terminal cover.
10) With the negative lead still removed, unscrew the bolt hightlighted in green. Remove the fuse from the yellow holder and then attach the yellow wire and tighten the bolt. As you can see I used the other one (not thinking) but will be moving it when I replace the battery.
11) Finally reattach the negative lead to the battery and tighten, the torque spec is 53 in-lbf (6.0 Nm or 61kgf-cm) (same torque spec on the positive lead by the way). Replace the positive terminal cover and insert the fuse for the hitch wiring and cover.
12) Start putting the covers back in place reverse of removal. When you get to putting the rear deck box in just run the hitch wiring through the cutout on the passenger side. I zip tied it to the the wiring harness that run along the back so it's secured. As you can see this is plenty of length to get out to a hitch. Continue to replace covers and you're done!
- Trailer hitch wiring by EVnut (Please note that he used a different product, my guess is the product I used wasn't available yet. I have to say he had a very clever solution.)
- Wiring discussion on PriusChat.com. Plus a great picture of a Prius towing a jet-ski!
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