Electrical

Approach

My Scrambler’s electrical system involved four primary systems:

• Engine wiring: My engine wiring harness came pre-installed on the LQ4 engine that I purchased from BD Turnkey Engines. The owner, Brian Dacus, and his son, Gage, reconfigured the factory wiring harness from the donor vehicle — in my case, a 2005 H2 — and re-installed it on the engine.

• Vehicle wiring: I initially planned to reuse my OEM wiring harness. I did a respectable job of removing it from my Jeep, meaning I preserved the full lengths of most wires and labeled them accordingly. However, as I began the re-install process, I realized that many of the wires were corroded and the bulkhead connections were dirtier than hell. So, I bit the bullet and bought a brand-new wiring harness, part #10150, from Painless Wiring.

• Gauge wiring: When I bought the Jeep and got it to run in it’s original/OEM state, I quickly realized that none of the factory gauges worked. Not one. Although I didn’t spend much time troublehshooting each gauges, I probably could have gotten them to work. But I decided to not even bother because they were in equally poor aesthetic condition — I needed to replace them. So, I invested in brand-new, direct-fit CJ gauge from Speedhut.

• Vehicle grounding: This was the simplest part of the electrical system. I used Painless Wiring’s universal body/engine ground strap kit, which ensures that “all electrical components and lamps get proper grounds by allowing direct paths to ground.”

I used aftermarket components for these three systems, and, as we’ll see, there were surprisingly few connection points among them. Installation was daunting at first, but things came together when I read the engine wiring harness and vehicle wiring harness installation manuals side by side — literally, side by side.

Engine wiring

BD Turnkey Engines reconfigures their wiring harnesses to meet the needs of your build. Seemingly across all their builds, though, you only need four wires connected “to actually start and run the engine.” These notes are from their wiring harness installation guide (which shows a few of my handwritten notes in the margins):

• Battery (orange, 12V+): This is a positive, full-time, 12V+ source. It is separately fused. Avoid routing this connection through a “master” kill switch. The ECM goes through a learning process every time this connection is lost.

• Ignition (red, 12V+): Generally from the crank/run side of keyed sources. It is separately fused.

• Fuel pump (blue, 12V+): This is the 12V+ from the fuel pump relay. The relay is controlled by the ECM and is separately fused. When the ignition is turned on, the fuel pump will cycle approximately three seconds and turn off until cranking begins. Run directly to fuel pump.

• Starter solenoid (purple, 12V+): This generally comes from the “crank” position of the key and what engages the starter to actually crank the engine over for starting. 12ga wire recommended.

Novak Conversions offers a comparable engine wiring harness modification solution. They, too, have four essential wires for constant battery, ignition/key-on, starter, and fuel pump.

Vehicle wiring

Since I used separate wiring for my engine and gauges, I only used the following components/sections of my aftermarket wiring harness from Painless Wiring:

• Harness power

• Front and rear lighting

• Trailer hook-up

• Under-hood, dash, and interior lighting

• Radio

• Cigarette lighter

• Blower motor

• Ignition wire

• Starter wire

• Horn

• Brake, 4WD, and reverse warning/indicactors

• Windshield wipers and fluid reservoir

Gauges

I used aftermarket gauges, all of which came with stand-alone wiring harnesses:

• Tachometer

• Speedometer

• Coolant temperature

• Fuel level

• Volts

• Oil pressure

• Transmission temperature

• Fuel pressure

Vehicle grounding

When it comes to grounding, I subscribe to the theory that “you can’t overdo it.” So, to properly ground my Scrambler, I ran grounding wires or straps between the following components:

• Battery (negative side) to engine block

• Engine block to frame

• Body/firewall/bed to frame

• Grill to frame

• Fenders to frame

• Dash to firewall

While not all of these grounds were strictly necessary today, in my view adding all of these grounding connections is a prudent step that helps future-proof the vehicle.