DIY Trailer Hitch Mount
 

I went to a single autox with my tires in the back seat and decided I didn't want to do that anymore. I bought a cheap trailer from Harbor Freight and started fabbing a trailer hitch based on this one by kask2_6.0. There were a few snags along the way but with kask's input it went pretty smoothly. Big thanks to kask2_6.0!

kask has registered as a vendor on the site and is now taking preorders, so I'm going to be very general in this guide and just point out the potential hangups that I ran in to. Anyone that is going to try to build a trailer hitch should already have the fabrication skills to figure out the rest. kask's units are CNC cut and pretty, so he's learned the lessons listed here and should make a very high quality piece that weighs in at right around 10lbs.

With a bit of trial and error, running a few errands and working at a semi-slow pace, we spent about 10 hours (before the wiring) on this today, so budget yourself a full day. If I wasn't in a rush and had known kask was going to sell these (I literally found out when I came in and looked at the thread during a brake from working on my own yesterday) I probably would have just bought one. But if this guide is ever useful to anyone, great.

The one hold up at this point is wiring. Using a typical light duty 4 pin trailer connector, I have no idea how to wire it correctly. I'll talk about it more later, but if someone could look at the what I've done and help me out I would really appreciate it.

http://www.3splooges.com/brz/13.jpg

So.. let's begin.

Prep work
- Make sure you have a safe place to keep your bumper cover while you work. I put mine on a movers blanket well outside of the work area.

- Measure how much clearance you have between the ground and the bottom of your bumper in the middle. You'll need this to determine how long of a receiver tube you'll need. On my stock suspension it was about 10".

- Also measure from your muffler to the furthest point on your bumper. This will help you determine how long the hitch mount needs to be. I didn't think to do this and ended up with a bunch of half-guessed numbers. I got lucky.

This hitch will be sandwiched between the unibody and bumper, providing a very strong, solid mount, and when it is complete will be completely hidden until you put a hitch in the receiver.


Removing the bumper

The first step is to remove the bumper and its cover. I forgot to get pictures of this step, but it is pretty well described in the Factory Service Manuals floating around.

- There are 8 clips along the bottom of the bumper cover. These are typical pry-up-in-the-middle push down type of clips. Start with those.

- 2 more clips (1 per side) in the wheel well, but they're a bit different to deal with as there is no head to pry up on. I pushed IN on the center of this clip and then pulled the whole clip out.

- 2 screws are visible when you open the trunk, just to the inside of the tail lights.

- Pull the bulbs from the backup light assembly and disconnect the looms clipped to the inside of the bumper cover

- Remove the tail lights. There is one clip on each side holding the carpet in place, 1 power harness plugged in and 4 nuts on lugs, then they slide right out.

- The bumper cover is kind of "zipped" in to place by a series of clips along the fenders and continuing under the tail lights to the trunk. Unzip these parts (a small screwdriver my help but be careful)

- The last remaining part is what the FSM calls 3 "guides" in the middle just below the trunk. I found I needed to get underneath the car and push up on a couple of tabs while my dad pulled on the bumper cover.

- Once it was loose, I crawled out from under the car and carefully moved the bumper cover out of the way.

With the bumper cover out of the way, there are just 4 bolts and 2 nuts to take off to remove the bumper. Note there are holes in the bumper that you can stick a socket with an extension through. I beat up my knuckles with a box end wrench before I noticed.

Fabbing the brackets

Now you should see this:

http://www.3splooges.com/brz/1.jpg

http://www.3splooges.com/brz/2.jpg

The 2 points under the bumper that are now showing primer are where the mount will be sandwiched. There is plenty of space between the bumper and the bumper cover for the extra materal we'll be adding. I'll spare the details for since kask will be building these but point a few things out for those of you that want to build your own. We'll make a bracket at either end:

http://www.3splooges.com/brz/3.jpg

Of note:
- I used 1/4" plate steel I had laying around and wouldn't recommend going lighter

- The hole in the center of the bracket is necessary to provide clearance for the tow hook mounting point on the back of the bumper bracket (see below)

- Each of the corners cut out of the bracket in the pic is also necessary (seams at the top and raise in the stamp at the bottom)

http://www.3splooges.com/brz/8.jpg

Then add a piece for the cross tube to attach to. This again was 1/4" scrap I had laying around, welded to the bracket square and with a nice strong corner bead. kask's prototype had gusseting and was much prettier than mine, and his brackets are water cut precisely and probably lighter. On mine, I didn't think to measure between the brackets on the bumper and ended up having to trim them (as can be seen above), so be cognizant of that.

http://www.3splooges.com/brz/4.jpg

Building the cross bar and receiver tube

Between the 2 brackets is a single piece of 1 1/4" tube stock, and the receiver tube will come straight out the bottom of this. Positioning of this tube is where the majority of your clearance issues will come up.

- With the receiver tube flush and plumb, you'll need clearance from both the stamped unibody and muffler below. Pictured is the stock muffler

- The backup light assembly is your limit in the other direction

In my case, I ended up with about 1/8" clearance to the muffler and about an inch to the backup light assy. If I were to start over I would move it out another half inch. The exhaust hangs on rubber hangers and will move, so I hit it a couple times with a ball peen hammer in the area of potential interference. Yeah.

http://www.3splooges.com/brz/5.jpg

After the cross tube was tacked in place I added my receiver tube. Before removing the bumper I measured 10" from the ground to the bottom of the bumper and needed to clear that. Also consider what you will use for a hitch mount and the height of the tongue on your trailer.

With the receiver tube tacked in place, we added some gussets, a reinforcing band around the end of the receiver and a couple of chain links for the safety chains.

http://www.3splooges.com/brz/9.jpg

While doing this, try to visualize how it will look when everything is put back together. In my case, the hitch mount pin is behind the bumper cover and above the safety chain hooks, making it difficult to get the pin in and almost impossible to get the cotterpin through that. My bumper cover is going to need some trimming and I've ordered [ame=http://www.amazon.com/gp/product/B0009V1WRU/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1]this[/ame] hopefully-easier-to-use pin.

Hitch mount and reassembly

Since we're working with pretty tight clearances all around here, and I didn't want to order parts, I bought a Curt 1 1/4" hitch mount and modified it to suit my needs. I believe it was 12" long.

We cut the tail end of the mount off and welded it to the top of the remaining part to make a vertical hitch mount adapter. 1 1/4" mounts are solid steel (instead of tubular) so this is the most uncertain weld on the whole project. We removed quite a bit of material to fill back in to make the joint as strong as possible.

http://www.3splooges.com/brz/10.jpg

http://www.3splooges.com/brz/11.jpg

The hitch mount and receiver tube really need to be worked out as a single unit. In retrospect, the tongue height on my trailer could stand to be an inch or two lower, and adding that much to my receiver tube would have made pinning the mount and hooking the safety chains easier. On the other hand, the receiver would have been hanging down below the bumper and visible. Adding a more common horizontal receiver tube is also an option and probably a good idea. but then it would be even more visible and potentially a shin-banger. You'll have to work out what you want to do here on your own.

Then, once everything was painted, we just put it all back together and tested. It works!

http://www.3splooges.com/brz/12.jpg

http://www.3splooges.com/brz/13.jpg

Wiring for lights

I used a simple 4-wire light duty trailer wiring kit to match my trailer. The best place to tap in is right at the left tail light - the right side splits out from there, so this is the only place you can find all of the needed wires. I guessed wrong when I did mine and cut right in the middle of the trunk, so I needed to cut again at the left light.

Here's a list of all the wires you'll find and their function:

Tail lights in car
- Red: Running lights
- White: Brake *
- Green: Right turn *
- Yellow: Left turn
- Black: Ground

* Fffffff. I thought I had this all sorted out but you'll want to confirm these 2 before doing anything. I'll doublecheck when I get home.

The issue is that that is 5 wires, but my wiring harness wants 4. The trailer combines brakes and turn signals to a single filament on the bulb and the turn signal is supposed to interrupt the brake light. The 86 doesn't do this -- the brake light and turn signals are on separate circuits.

So you'll need 3 wire to 2 wire convertor like this: http://amzn.to/16iyTTd

Simple enough. After I cut my OE wiring harness I soldered in a pigtail beween the 2 sides to give me a bit of length to work with. I didn't cut the black ground wire; I instead crimped on a ring terminal and grounded it to the body. There's a point toward the middle of the trunk that already has a couple grounds on it.

Now you're just matching function to function. Unfortunately the colors don't quite match.

Wiring harness
- White: Ground
- Red: Running lights
- Green: Right turn
- Yellow: Left turn

After everything was soldered and wrapped I zip tied up all of my wires and added a couple more zip tight ties to a hole in the chassis so I won't be pulling on my soldered joints. I didn't want to drill any holes (or use the hole already in the bottom of the trunk with a plug in it), so the harness stays in the trunk when I'm not using it and just hangs out when I am.

Reserved.

subbd

What are you hitching?

That's all I care about.

If you read it is pretty apparent that it is tires/wheels.

Its a clever idea but its not even mounted onto the frame of the vehicle. As soon as you attach something, your hitch is going to fall off the vehicle.

Fall off? It's bolted to the frame rails. Probably shouldn't tow your ski boat with it, but a small utility tailed would be perfect.

Awesome job op, I have a new project for my dad and I to work on now. We did something similar to my srt4. It was hilarious to see the looks from people when you're towing a dirt bike with your car.

Looks like the muffler is dented. If so that's my only complaint. Looks like some real quality work!

http://www.3splooges.com/brz/16.jpg

The muffler was just close enough that it was probably going to rattle so I hit it with a ball peen a couple times. It's not visible, won't affect performance and I'll replace it before long anyway. The receiver tube could be moved out another quarter inch but that would make pinning the hitch even more of a pain. Small price to pay to put tires on my trailer instead of in and out of the back seat every week and hours of driving with my knees in my chest.