Wiring a race car from scratch doesn’t have to be hard

We needed to rewire our Mustang from scratch but, fortunately, we had some help: We threw away the 60-year-old harness and replaced it with a Ron Francis Wiring Bare Bonz harness kit. This move also saved weight while reducing complexity.

The Bare Bonz wiring harness was essentially laid out custom for our project. Ron Francis gives you enough leads and length in this $379 kit to do this easily.

Another major benefit, though, is this kit provides three relays and eight fused circuits with modern fuses. You decide what you want to fuse and what needs relays. In our case, for instance, we needed a relay for our Derale electric cooling fan. 

Ideally, the fuse panel should be mounted low, cool and dry. You should also try to keep your wires short to save weight.

We put ours behind the original glove box door, an open area since we removed both the glove box and the heater. This location was a good compromise for a dry, central, easily accessible location.

We then mounted our MSD 6AL ignition box right next to the fuse panel for all the same reasons. (The coil is wired through the MSD ignition box, and the MSD is powered through the ignition switch.)

We cut the area to the left (center) of the glove box a bit to give us even better access to the ignition module should we need to change redline chips. (We started with a 6500-rpm chip but could go to 7000 rpm once we break the car in a bit more.)

We ran all of our wires out of the back of the panel for easy access to the firewall so, as needed, they could also run down the passenger-side rocker panel.

We also wired in lights and a rain light for night racing, as we’d like to run HSR’s Classic 24 at Daytona. Plus at least one brake light is required by all sanctioning bodies. Our brake lights run through a Wilwood mechanical pressure switch. (Trust us, we have learned the sight of a black flag thanks to wonky old brake light switches.)

We also needed a kill switch, so we picked up a digital model from Cartek. Unlike a traditional, old-fashioned master switch, the Cartek piece doesn’t feature any moving parts. All power switching is fully electronic.

This unit fits between the negative side of the battery and the chassis. When the external kill button is activated–we have one on the outside of the car and one for the driver–a battery isolator shuts down the negative terminal, quickly disconnecting the entire electrical system.

We also needed to hook up our fuel gauge. The sending unit for our Fuel Safe cell is located inside the unit, and we just had to calibrate it to our fuel gauge. (Prosport also makes a sending unit for its own gauges.)

One more thing to consider: We wanted a power source for data acquisition, cameras, etc. And you want that power unswitched so turning off the engine doesn’t shut down all of these electronics. We used the optional Ron Francis Wiring switch panel to simply wire our cigarette lighter with two adjacent USB ports that we picked up at our local auto parts store.

When wiring, of course, make a wire diagram–and keep it–and label your fuse box and switch panel so you can quickly diagnose any issues. To dive deeper into wiring a race car, read this related story: [How to wire a car from scratch]

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