Kill The Gremlins! Five Foolproof Project Car Wiring Tips

Building an engine can be fun, and installing it into your pride and joy can also be a labor of love. Motorsports wiring? Most people don’t love this part of the automotive hobby, and we suspect this is because many don’t have the background in electrical systems and their respective requirements to ensure consistent performance. But our friends at EFI University do–and they are willing to share their expertise with us. Without further ado, we present the five things you want to do when setting up your new project engine into its new home.

Do Understand the Fundamental Laws of Electrical Physics
Basic laws of physics like Ohm’s Law will help to guide your project component selection and even system selection in some cases. We find most projects are always centered around some system or component that we must make work with the rest of the design. Things like ignition coils and ECU injector drivers can bring a project crashing down when we don’t plan for what the total system requirements will be!

Organize Sensors, Actuators, Controllers, Fuses, Relays, and Switches Needed
Proceeding from the first point, we go deeper into the process of building the system. When we don’t have a clear plan of what all the needed components will be, it makes for a terrible time implementing a masterpiece product.

Carefully and methodically list out and write down each of the necessary components for the systems to be installed into the vehicle. Do this for each system such as: Engine, Transmission, Chassis, Suspension, Brakes, Module Communications, Driver Communications, and other components.

Calculate Maximum Circuit Load for Wire Gauging and Fuse Selection
Once the systems and components are organized, it’s time to look at what type of loads each of the items may bring to the project. If we know we have a starter or fan or fuel pump which will draw a large amount of amperage, we want to plan to get properly sized wire to make the item function as intended.

With a little more fundamentals of physics, we find that the wires used in each system will resist current flow and as such, we see a reduction in voltage at the load source (Voltage Drop). If a specific amount of current or voltage is required to make the circuit work, then dialing in on reducing voltage drop across the circuit will be critical!

Crimping joints has its place, as does the use of solder.

Plan System Functionality and Behavior
Assuming all your circuit loads and wire lengths and fuse capacities are calculated, you would generally want to plan your system functionality.

It kind of feels like we’ve been doing this already, but what I mean here is as follows:
I have a starter motor to turn. I need a battery cable and a good engine ground but need to send a signal to the starter solenoid to complete the circuit and get the starter to spin. Easy! I’ll put a high current push button in the dash panel and run an 8-gauge wire to the starter solenoid input.

This would work beautifully to engage the starter, and most systems would be wired in a similar fashion for simplicity, but… This means that any time you push the starter button, the starter motor will attempt to drive the flywheel. I can tell you that most starters I have tested do not care to attempt tooth engagement when the other gear is spinning at a million miles per hour!
Another point I feel the need to share is that if you are wiring a drag car that needs a starter bump button in the engine bay, design the circuit so that the button is dead/inactive when any of the fuel or ignition related systems are switched on. And maybe include a removable activation connector on a little tether cord so that it can be manually over-ridden when servicing the engine or transmission. This is a general courtesy to anyone who is going to be working around the flywheel or drive belts to ensure they are safe.

Poor planning will get you poor results!

Haste Makes Waste So Slow Down, Sally!
The last item to mention is that while a speedy service is always a remarkable thing, when we get in a hurry on a project, it normally ends up costing us more time and more money. It’s all too easy to get ahead of where you need to be. When you are building a motorsport harness, it’s hard to get labels on your leads when there is a large connector or transition in the way! Do every section of the harness in a step-by-step, “What comes next” sequence. Connectors and terminals can generally be put on last to avoid missing some shrink-tube, labels, or a transition/boot.

Especially for you shop owners: If you know you are out of supplies and will need at least a week to get the order shipped in, don’t promise your customer the job back in a week’s time! This frustrates the customer when the deadline keeps getting pushed back and puts extra stress on you and your staff. Things take time, so plan a little extra time for testing the project before delivery. Don’t over-promise and under-deliver.

Thanks to EFIU’s Eric Demyan for compiling this list!

If you are interested in learning more in a hands-on environment, EFI University is hosting its Motorsports Wiring & Configuration course at its Lake Havasu City, AZ location from August 28-30, 2017.

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About the author

Jason Reiss

Jason draws on over 15 years of experience in the automotive publishing industry, and collaborates with many of the industry's movers and shakers to create compelling technical articles and high-quality race coverage.
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