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  • JP Magazine
  • Dirt Sports + Off-Road
  • 4-Wheel & Off-Road
  • Four Wheeler

Tips to rewire your vehicle like a professional

Posted in How To: Electrical on March 4, 2016
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Everyone loves big tires and coilover shocks. These are like the bulging biceps and six-pack abs of the off-road world. Wiring, while not as glamorous, is the nervous system that keeps your whole vehicle running. Without proper wiring, your functional 4x4 turns into a really cramped mobile home because it isn’t going anywhere. Recently, we tackled the wiring portion of a large project where 1-ton axles and coilover shocks had already been added and the bodywork was complete. It was time to make the flatfender buggy run, so we made a call to Painless Performance.

Painless had everything we needed to get our small-block Chevy-powered Jeep running. From big ticket items like its Off Road Harness and TBI engine harness to ground straps, battery cables, and PowerBraid wire loom, Painless has it all. The harness uses high-quality thermal cross-linked wire with each wire labelled every 6 inches. And the Off-Road Harness that we chose is weatherproof, with a triple-edged gasket on the front of the panel and each wire completely sealed on the back, making it perfect for the harsh conditions we often encounter. Once we decided how many circuits we needed and the components showed up, our job wasn’t done though.

Wiring is a time consuming job that requires patience and detail in order to ensure success. We laid out the entire wiring harness and determined where we were routing each wire, a step that isn’t nearly as involved if you use one of Painless Performance’s custom harnesses for Jeeps, Broncos, and Chevy trucks. We didn’t use any Scotchloks on this install. We instead each wire was crimped with one of the high-quality terminals and heat shrunk for reliability. And once the wires were routed, we took care to insulate them from heat, vibration, and anything that might cut or fray the wires. The hard work resulted in a nervous system that allows us to reliably put our 40-inch tires and coilover shocks to work on the toughest trails without concern. Now if Painless could just help us with those six-pack abs.

How Many Circuits Do You Need?
Even on a simple rockcrawler like this, we ended up using nearly all of the circuits in the Off-Road Harness. A more modern vehicle would have even more circuits. Before purchasing a harness, consider the following and leave space for items that you don’t have now but might add in the future.

Brake Lights
Turn Signals
Auxiliary Lights
Rock Lights
Interior Lighting
12V Power Outlets
Electric Fan(s)
Fuel Pump
Fuel Injection
Electric Choke
Power Windows
Power Door Locks

Top Wiring Tools
Test light/Multimeter
Wire Strippers
Wire Crimpers
Diagonal Cutters
Step Bit
Butane torch

We chose Painless Performance’s Off-Road Harness with 10 fuses and 4 relays. Note how the wiring is completely sealed to ensure a safe, reliable connection. This completely customizable harness provides 10 fuses, two 40-amp relays (perfect for operating things like electric cooling fans or fuel injection harnesses), and two 20-amp relays for lights, fuel pump, or water pump.

The relays in the Painless Off-Road Harness are housed within a weatherproof fuse block that does an excellent job of sealing out water and dirt. Water and electronics don’t mix, but if you are like us that doesn’t stop you from enjoying the mud. This weatherproofing gives us peace of mind in harsh environments.

Before laying out a single wire, we made a diagram of our installation with each circuit and where it needed to be routed. It was much easier to make changes to this figure than to reroute wires after making an error during the installation. Patience is key when performing a large wiring job like this.

Painless even carries what you need to make your own battery cables. This was perfect for our Optima YellowTop battery, which is located under the passenger seat of this stretched flatfender. We filled the terminal rings with melted solder and then inserted the fine-strand wire and crimped it for a durable connection. Then we used heat shrink from Painless to complete the battery cables.

Vibration is a killer for wiring, including battery cables. Rubbing wire can wear through the insulation and cause a short or even cause the internal copper strands to fatigue and break. For this reason, it is best to secure all wires to minimize movement.

All of the connectors you need to complete the wiring installation are included from Painless. These are high-quality connectors complete with heat shrink, making soldering unnecessary.

A quality pair of wire crimpers is a worthwhile investment if you are rewiring your entire vehicle. Plus, who doesn’t appreciate nice tools? These Snap-On crimpers are made in America and can both strip wire and crimp connections reliably and accurately.

Painless only uses thermal cross-linked wire with thin-walled insulation that makes the wire both physically smaller and more flexible. This translates into wire that is easier to route and install.

This flatfender is running a small-block Chevy and TH400 transmission. The tranny doesn’t require any electronics, but the engine does since it is running throttle-body fuel injection (TBI). While it doesn’t make as much horsepower as sequential port injection, TBI runs better at angles compared to a carburetor and is the cheapest and simplest choice for fuel injection. Painless Performance makes a specific TBI harness that includes a detailed step-by-step manual, and GM color-coded wires with labels for all sensors. You provide your own ECM.

The TBI harness from Painless Performance comes with an OBDI port and check engine light. These GM systems are far simpler than later OBDII systems, but the port still allows us to read basic codes and retain emissions legality. That is not an issue for our dedicated rockcrawler, but it may be an issue on your project.

One of the details that set Painless Performance apart from other wiring companies is its comprehensive instructions. They thought of everything for our universal off-road harness, and the application specific harnesses for Jeeps, Broncos, and pickups are even more thorough. If you still have a problem, help is just a phone call away

We like to use Weatherpack connectors because they do an excellent job sealing out the elements and you can disconnect and reconnect them easily with minimal wear. They do require a special crimper though to install, so keep that in mind if you plan to use Weatherpack connectors on your own wiring installation.

A 200-amp MIDI fuse comes prewired on the Trail Rocker so there is no need to worry about how to crimp that 6-gauge power cable. Other details include a gasket to keep moisture out of the relay center and stainless hardware fit with O-rings.

The Trail Rocker allows you to control up to eight accessories and has a weatherproof housing that surrounds the power center with eight fuses and relays. If you own a JK, you are in luck, as Painless Performance designed the Trail Rocker specifically for JK Wranglers with a prewired switch panel. By the time you read this, though, Painless Performance will have a universal Trail Rocker available.

Painless Performance includes circuit breakers for the six circuits in their switch panel, but since we ran the wiring to the Trail Rocker, we replaced the circuit breakers with indicator lights from Painless. A variety of labels are included so you can customize the installation for your specific needs.

We combined the Trail Rocker with this switch panel from Painless Performance. The switch panel includes a keyed ignition switch, which was appreciated on our custom flatfender buggy. A formed polyethylene liner seals the faceplate to the interior panel between our front seats, creating a water-resistant barrier.

We bundled our wires together with plastic cable ties every 4 inches or so. This not only keeps the wiring tidy but also prevents loose wires from being subjected to strain. If you ever look at the wiring of an off-road race car, you will find the installation is very similar to this.

Painless Performance wiring harnesses come with wires that are labeled every 6 inches to make installation, well, painless. They even use black ink on light-colored wires and white ink on the dark wires. We used a universal off-road harness, but Painless offers custom fit harnesses for most popular applications that make installation even easier.

Prior to completing the installation by bundling all of the wires together neatly and covering them in PowerBraid, we tested each circuit to ensure that it was functioning properly. This is a useful step to identify and resolve any issues early in the installation process.

You can start with the best harness, but if it is installed poorly, you will likely experience problems in the future. Note how a grommet was used to pass the two wires through the firewall without concern about them chafing and potentially shorting out. Also visible is heat shielding that helps fend off the high temperatures produced by the nearby engine.

PowerBraid is a flexible sheath with a tough woven texture that protects the insulation of any electrical wire bundles or cables. It is available from Painless Performance in a variety of sizes and has a melting point of 482 degrees, making it perfect for use under the hood. It uses a split loom design for easy installation after your wiring is installed, but has a minimum overlap of 25 percent for optimum protection.

How A Relay Works

Relays control one electrical circuit by opening and closing contacts in another circuit. There is typically an open contact when the relay is not energized (although some relays are in a closed stage at rest), but applying electrical current to the contacts will change their state. Relays can control large amperage draws by having an amplifying effect because a small amperage applied to a relays coil can result in a large amperage being switched by the contacts. Anything that draws more than 25 amps should be run through a relay. Examples include electric fans, winches, and electric fuel pumps. Protective relays like Painless Performance uses in their Trail Rocker can prevent equipment damage to your vehicle by limiting the amount of amperage through the wiring harness inside the vehicle.

A standard five-pin relay has a single control circuit but two separate current paths for the switch: one when the relay is de-energized (no current through the control coil) and the other the energized (current is flowing through the control coil). When the relay is de-energized (off), pins 4 and 5 have continuity. When the relay is energized (on), pins 3 and 5 have continuity.


Painless Performance Products
Ft. Worth, TX 76105

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