How to Install a Wire Harness

Harnessed wiring
At first, glance, installing an aftermarket wire harness may appear to be a difficult operation. Some may even cringe at the concept; after all, our time in the garage is supposed to be enjoyable, isn’t it?

How to Install a Wire Harness

However, if you’ve ever attempted pricing out a bespoke wiring harness from a professional garage, you’ll know that the 20hr labor price can quickly change your mood. The truth is that kits were designed with the do-it-yourselfer in mind. Most intended harnesses to be a weekend effort for the ordinary street rodder. Every kit comes with a full set of step-by-step instructions, as well as pre-labeled circuits. And with a little work and patience to carefully follow the instructions, taking each circuit one step at a time, anyone can do it.

Choosing a Harness

When you’re ready to buy a wiring harness, there are a few things to think about. To begin, assess the number of circuits required for your application. On a T-bucket application, a basic 8-circuit harness is usually all that is required. A 12-circuit harness is appropriate for a wide range of early street rods that just require basic needs such as ignition, horn, lights, charging, and so on. Planning is also vital; if you intend to add power or air conditioning in the future, a 12 or 22-circuit harness would be preferable.

Advice on Getting Started

If you’ve never wired a car before, getting started can be one of the most difficult tasks. You can always begin by putting your harness out on the floor. Make yourself acquainted with the various wires and circuits. Then organize them into the major wire groupings, such as the dash, instruments, switches, engine, headlights, and taillights.

Then you can choose where to install the fuse block. Customers typically screw the box to a bracket or the body of a fiberglass automobile. The fuse block is usually best mounted under the dash on the firewall, but some people prefer to position it under the seats. You’ll want a location that’s easily accessible and will make it easier to run the cables from the front to the back of the automobile. If you removed an existing harness from your vehicle, keep it in case you need to re-use certain pigtails or connectors for your vehicle.

Beneficial tools

A good stripper/crimping tool will make a big impact, especially when it comes to solderless connectors. To protect and insulate the wires while maintaining a clean appearance, apply heat shrink tubing over the connectors. To secure the wiring bundles to the firewall or frame, standard wire holders can be used. Finally, after you’ve finished, a test light is essential for fine-tuning the entire system. This allows you to test for any voltage leaks or shorts that may occur after the installation.

If you’ve never wired a street rod before, don’t worry; there are lots of helpful resources available, such as our book “How to Wire a Street Rod.” It walks you through the process of wiring up your rod step by step with clear detailed instructions. In addition, if you’re working on a car from the 1950s or 1960s, you can always refer to the factory repair manual for specific instructions for your vehicle.