DIY/How-to: Wire Your RRC for a 4-flat Trailer Without Splicing Wires or Paying Through the Nose
I hate splicing or tapping into vehicle wiring harnesses. As I build out my rig, my goal is to keep as many of my electrical modifications free of splices into the vehicle harness. First installment in the series: wiring in a 4-flat trailer connector without paying $90 for an adapter from Atlantic British. All pictures can be enlarged by clicking on them.
I believe all NAS RRCs are wired with the body tow harness already in place. It's under the right quarter panel and is a round connector with a rubber cap. When you remove the cap, you'll notice that it's a small 7-pin round connector that conveniently is not compatible with either the US or the Euro 7 pin round trailer kits, so you can't use anything off-the-shelf from Uhaul or your local trailer shop.
You'll need the following parts:
- A trailer wiring converter for cars with separate turn signals and taillights (http://tinyurl.com/k9derp2)
- 4mm/.157" male bullet terminals (https://flic.kr/p/syrbLW)
- 4mm/.157" female bullet terminals (https://flic.kr/p/sj99cs)
- Multimeter or test light
- Crimping tool
- Sharp wire cutters
- Zip ties
- Phillips screwdriver
- Allen key if you have rear brush guards
- Optional: heat shrink tubing, heat gun, electrical tape
Total cost is about $20.
The process may seem daunting but it actually goes very quickly and is straightforward. The time consuming parts would be the same with the proper converter box or the DIY method, which is mounting the converter box somewhere out of the way and routing the wiring.
Remove the taillight and feed the Rover trailer connector up through the taillight mounting hole. This way you can mount the box up inside the quarter panel where it's safe from water and dirt. Find the deep set phillips screws and remove them (the small ones are just for the lens, not the whole assembly). If you have brush guards you'll need to remove them first with the Allen key.
Now, here's your Uhaul converter box. Your taillights, brake lights, and turn signals are all on separate circuits on your car, so we need to combine them for the trailer. That's what the box does. You have input from the vehicle, and output to the trailer which has the 4-flat built in (with convenient test LEDs).
On the vehicle side of the converter box, strip the ends of each wire and crimp one female bullet connector onto the end of each. Optional - slip a piece of heat shrink that is just barely wider than the Rover round connector onto the vehicle-side converter wiring to waterproof the connections later.
Snip your male bullet connectors with the wire cutters to remove the insulated bases and leave just the metal bullet tips. You will need to slide these onto the pins on the Rover connector so the female bullet connectors have something large enough to fit with. It should be a tight fit, if not, you'll need to squeeze them a bit before putting them on so they don't fall off. I slid them over all the pins since I did it before testing circuits - I haven't decided if that was good or bad. It made a tight fit for all the connectors which put more pressure on the pins than I'd like, but I think it will make the connections less likely to vibrate loose. Up to you how you do this.
Now use the multimeter to find out which pin on the Rover connector is which circuit. Left signal, right signal, tail lights, brake lights. A helper is useful here to activate the signals, lights, brakes, etc. Pretty simple, your multimeter will show 12v when that circuit is getting power. For the signals, you'll get spikes to 12 and drops to 0 as the signal blinks. If you have a cheaper multimeter, it won't keep up so you'll see erratic readings jumping around. This is the same thing, it just can't keep up with the voltage switching. As you figure out which circuit is which, slide the female bullet connector for that circuit (which is labeled on the wire and the instructions that came with the converter) onto the pin.
Slip the converter box back into the area behind the taillight loosely for now. You'll notice the taillight harness comes through the body from the interior. Feed your ground wire through the grommet the taillight harness uses. You'll notice in the back near the amp is a ground screw - perfect! Loosen the nut a bit and slide your ground wire's spade connector into it, and tighten the nut down again. This is just above the amp in the right side of the load space. The ground wire on my kit is the white wire with the red tag on it.
Now you're all wired in! Grab your helper again and have them activate each signal, brakes, and tails. The test LEDs on the flat-4 connector should each light up with the appropriate circuit. If that works, great! Time to button it down.
First, slide the heat shrink tubing that you put in place earlier over the Rover connector so it covers the bullet connections and heat it up so it shrinks. Wrap some electrical tape around the end that goes over the wiring since it likely won't shrink down enough to secure and waterproof them.
Feed the converter box and Rover connector up into the quarter panel. It will sit up there pretty nicely and be reasonably protected from the elements. The 4 flat connector goes down under the body and you can choose how to route this yourself. I still need to find a better way of routing mine. ZIP tie the extra slack in the 4-flat connector in different places as you see fit so you have just the right amount to get to the hitch receiver.
Reinstall the taillight and brush guard. ZIP tie your 4-flat connector near the receiver hitch. Clean up your supplies and drink a beer!