Introduction: How to Build a Utility Trailer From a Kit

About: The official instructable for Popular Mechanics magazine, reporting on the DIY world since 1902.

Sure, pickup trucks are great. Trouble is, all that cargo space is just so much decoration on the daily commute. And forget about trips with the kids and dog. For many of us, the family car is just too practical to replace with a utility vehicle.

Fortunately, you can have your utility space and passenger-car comfort with a light-duty trailer. It’s really the best of both worlds. And fun. We built the NuWay Model No.NW13848BF trailer kit made by Hunter Technology, P.O. Box 100, Orillia, Ontario, Canada L3V 6K1. NuWay trailers come in a range of sizes and designs, and the units are available partially assembled as well as in do-it-yourself kits. 

Our trailer is 51 x 96 in., making it useful for hauling 4 x 8 plywood and other large construction materials, and it folds for easy storage when you don’t need it. It has a payload capacity of 1300 pounds, 8-in wheels, and a list price of about $305. The kit comes with everything you need except material for the bed.  You can buy this trailer 85% assembled, with a plywood bed and 12-in wheels, for about $509.  A smaller model and a boat trailer are also available.  (Editor's Note: while this product information dates to 2001, the process of building a kit trailer is still useful if you're using another kit, or designing your own trailer.)

This project was originally published in the May 2001 issue of Popular Mechanics.  You can find more great projects at Popular Mechanics DIY Central.

Step 1: Build the Frame, Part 1

First, slide each hub with its inner bearing onto the axle, and then add the outer bearing, washer, castle nut, cotter pin and cap (Photo 1). Set the axle aside and begin work on the frame by bolting the coupler to the tongue (Photo 2).

The trailer is made of two similar ladder frames joined with hinge plates that allow the assembly to fold. Following the plans in the manual, assemble both frames upside down with bolts, washers and nuts (Photo 3). The crossmembers of the frames are U-shaped with flanges facing up (the frames are upside down), and they have two bolt holes at each end.  Only install bolts in both end holes of the trailer’s front and rear crossmembers. At the four other crossmembers, leave the bolts out of the flange holes for now. When the frames are together, add the tongue channel and the two diagonal braces (Photo 4). The ends of the braces are bolted through the open holes in the middle flange of the front frame.

Align both frames on two lengths of 2x4 stock that span a pair of sawhorses.  Then, mount the offset hinges on each side of the front and back frames (Photo 5).  For now, don't tighten the fasteners.

Step 2: Build the Frame, Part 2

U-shaped channels called carriage frames are used to stiffen the hinged frames on each side so that the trailer is a structural unit when open. Before securing these channels, install a bolt in both ends of the front flange of the rear frame, and add another on each side in the next hole along the side rails. These bolt heads act as aligning bosses for slots in the carriage frames. Place the carriage frames over the 1⁄4-in. bolt heads on each side. Next, fasten the carriage frames to the front trailer frame with two bolts on each side (Photo 1). 

Place the springs in the carriage frames with the spring eyes toward the front. Install spring-retaining bolts, with fender braces placed under the bolt heads. At the back of each spring, add an anchor plate on each side (Photo 2). This plate locks te it with U bolts (Photo 3). With all of the components in place, double-check that the frames are square and tighten all fasteners.  Then, assemble and install the stands that will support the trailer when it's folded (Photo 4).

Step 3: Electrical Work

With the wheels in place and the trailer flipped upright, attach the taillight brackets to the rear side rails, and secure the rear lamps with nuts. Attach the side lamps with bolts that pass through the side rails (Photo 1). Use lockwashers under the bolt heads inside the rail. These bolts are the ground connections between the side lamps and the frame. Make sure the lockwashers bite into the metal for a good connection. Now you can install the lenses. 

The wiring to each side is in color-coded pairs: green and brown for the right and yellow and brown for the left. String the wiring from the rear lamps to the tongue, allowing extra wire at the hinge point so the trailer can be folded. At the front, attach the white ground wire from the wiring harness to the frame with a screw at a hole near the coupler (Photo 2). 
To wire the side lamps, first separate the paired wires near each lamp. Then, snap splice cone wire ends, and press the color-coded wires into the labeled connector holes (Photo 3). 

Follow the kit’s instructions for wiring the harness in your car. When the wiring is complete, plug the trailer harness to your vehicle’s harness and check that the lights function properly.

Step 4: Finishing Up

Install the plastic fenders by bolting them to the fender brackets (Photo 1). Then, cut the plywood to size for the bed. Lay the pieces on the trailer and mark the screw locations to match the holes in the frames.. Bore holes for the screws, and varnish both sides and all edges of the plywood with three coats of spar varnish. Then, install the panels with self-tapping screws (Photo 2). 

You can buy various accessories for your trailer to suit your hauling needs. For our model, a motorcycle rail, wood rack and metal cargo box are available. We opted for the wood rack (about $135). The rack sections come preassembled, along with necessary screws and brackets. Place the sections in the stake slots of the trailer rails and screw the components together (Photo 3). 

To fold the trailer, remove the bolt in each anchor plate at the rear of the carriage frames. Then, pivot the rear trailer half up and onto the front half (Photo 4). Secure the halves with the supplied hardware. Lift the trailer at the tongue so it rests on the stands. Remove the pin in the tongue and fold down the tongue.

Congratulations, you've created a functional and durable trailer.