If there is one area of mysticism and witchery on a 4x4, it’s in wiring and electrical upgrades. Interestingly enough, the wiring is often the area where we see incredibly butch and scary-hack modifications on a 4x4. In most cases, the horrendous handiwork is hidden under the hood or dashboard, waiting to cause parasitic battery drain or worse, a car fire. The good news is that wiring is actually fairly simple on older 4x4s, but on newer 4x4s it’s so complex that any modifications usually involve the addition of a completely separate simple wiring harness.
The easiest way to understand the electrical system of your 4x4 is to think of electricity like water. Both water and electricity generally travel the path of least resistance. For this example, think of your battery as a lake and your alternator as the river feeding that lake. The lake (battery) holds a finite amount of water (electricity), and you can only drain it so far before it goes dry (dead) without refilling. The river (alternator) replenishes the lake (battery), but it can only do so at a set rate. Draining the system beyond its capability will result in a dead battery, even with the vehicle running. The electrical upgrades that you should make to your 4x4 will depend on the kind of demands you place on the system. Here are a few tips to keep everything on your truck or SUV electrified.
It’s not uncommon for a traditional wet-cell battery to get banged around off-road in a 4x4 and leak acid all over an engine compartment. The acid makes an incredible mess in a short period of time. An AGM battery like the Optima Batteries (optimabatteries.com) YellowTop will not leak. The acid inside is a paste, so even if the battery is mounted upside down, it can’t spill. Winches, off-road lights, large stereos, portable refrigerators, and other electrical devices can regularly draw down a battery, making deep-cycle batteries like the YellowTop a better choice than a RedTop for a 4x4.
Even a few add-on electrical accessories can overwhelm the 30-60 amp alternators commonly found in older 4x4s. Companies like DC Power Engineering (dcpowerinc.com), HO Alternators (highoutputalternator.com), Nations Starter & Alternator (nationsstarteralternator.com), Powermaster (powermastermotorsports.com) and Premier Power Welder (premierpowerwelder.com) all offer bolt-in high-output alternators for both older and newer applications. Some of these alternators are designed to produce up to an impressive 300 amps, which should be more than enough to keep the battery in an average 4x4 fully charged.
If you plan on heavy winching or running the lights or stereo with the engine off for long periods of time, you should seriously consider adding dual batteries. They can be isolated so that no matter how far you run down one battery, the other will always be fresh and ready to start your 4x4. Companies like Rugged Ridge (ruggedridge.com), Smittybilt (smittybilt.com), and Wrangler Power Products (wranglerpower.com) offer dual battery kits for popular 4x4 models. Some fullsize truck applications have optional dual batteries available from the factory, so you may be able to use OE parts in your conversion.
Factory dual alternators are available for some truck and engine combinations. If you are a real power junkie, you can add dual alternators to almost any vehicle with bolt-on kits from companies like DC Power Engineering, HO Alternators, and Nations Starter & Alternator.
Most modern 4x4s don’t have a lot of available real estate in the dashboards for multiple electrical switches. Companies like Painless Performance Products (painlessperformance.com) and sPOD (4x4spod.com) specialize in complete switch panels with fuse-protected harnesses to simplify the installation of multiple lights and other switched electrical devices. Painless Performance also has complete vehicle wiring harnesses for popular older 4x4s.
The plastic ATM, ATC/ATO, and MAX blade fuses are best used on low-amp draw devices. Heavy-draw items like air compressors and electric cooling fans that require 20 amps or more can melt the universal inline fuse holders commonly used with these fuses. Circuit breakers are a better solution for protecting the wiring of high-amp draw devices.
Companies such as Bussmann (cooperindustries.com) and MP (mechprod.com) offer heavy-duty waterproof and marine-grade circuit breakers to accommodate 25-300 amp loads. If you overload the circuit, there is no need to replace a fuse—you simply reset the switch. This can be a really handy feature if you are out in the sticks a long way from replacement fuses.
Any electrical device that requires more than a few amps should be switched via a relay. A relay is an electric-actuated high-current switching device that is operated by a low-current switch. This keeps the high-amp wires out from under dash where they could do a lot of damage if an electrical short occurs. Automotive relays are available in all shapes and ratings from 5 to more than 500 amps. The 15-40 amp five-prong plastic horn-type relays are the most common and can be wired in several different ways for switching power to electrical devices.
AGM-type batteries like the Optima and others don’t always fit snugly in factory battery trays. Companies like Blue Torch Fabworks (bluetorchfab.com), Camburg (camburg.com), RuffStuff Specialties (ruffstuffspecialties.com), and others offer heavy-duty steel trays for AGM batteries that can be easily adapted to your 4x4.
Headers and tightly routed exhaust can cause a starter to become heat soaked and sluggish, while high-compression engines need more oomph than a stock starter can provide. Gear reduction starters like those from Powermaster can cure common slow-cranking issues.
Carefully route wires away from heat sources and moving components. Neatly secure the wires with zip ties and wrap them in heat-resistant wire loom for extra protection against chafing. Use rubber grommets to protect the wires when routing them through the firewall or other body panels.
Battery cutoff and dual battery isolator switches are available from most marine and automotive racing suppliers. The keyed versions (pictured) can work as a primitive, yet effective theft deterrent, especially if the switch is hidden.
The Premier Power Welder is probably one of the most versatile electrical devices you can add to a 4x4. The kit includes a high-amp alternator and gives you the ability to make trail repairs with a built-in 100 percent duty-cycle DC welder; power 115V brush-type devices such as grinders, drills, saws, and incandescent lights; and quick charge a dead battery. The welder and alternator kits are available for nearly every truck and SUV application.
Electrical current is measured in amps. Each electrical device on your 4x4 requires a specific number of amps to run, although some devices like electric fans may draw significantly more power when first turned on. Conveniently, your alternator’s output is also measured in amps. You can add up the amp draw of your accessories and compare it to the output of your alternator to see if you are draining the system beyond its capability. Below are some common automotive electrical devices and their amp draws.
|52-inch LED lightbar||20-40|
|Electric air compressor||5-50|
|Electric cooling fan (each)||10-30|
|Electric fuel pump||7-15|
|Radio, CD player||3-7|
The multi-strand copper wire used to power automotive accessories comes in many different sizes, grades, and ratings. Drawing too much amperage through too small of a wire can let them smoke out and cause a fire, not to mention make a mess of your wiring harness. Match up the proper gauge wire with the amp draw you have planned for it. Below are some common wire gauge sizes and their ampacity (amp rating). Wire smaller than 18 gauge usually isn’t recommended for wiring automotive accessories regardless of electrical current demand. Small wires can be easily damaged.