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Image above courtesy Painless Performance. All images by Enilda Aguilar unless otherwise noted.
Wiring is the one area that most hot rodders despise out of everything involved with a restomod or race car build. I’ve seen some cringe-worthy hot rod wiring jobs in my time. I’ve also seen some that are done so well they should be in the Smithsonian. I’ve learned a thing or three about how to properly wire a vehicle and I’m going to impart some of that knowledge to you.
Begin by laying everything out. Whether you’re installing a car stereo or whole chassis wiring harness, you need to lay everything out before doing anything else. This will give you an idea of the scope of what you’re diving into and will also allow you to compare what you’ve got with what the documentation says you should have.
Study the installation instructions and determine where components are going to go and where wires can and should be routed. Route planning is especially important when there are firewall/bulkhead penetrations to be made. You want the minimum number of penetrations possible and they all need to be protected, as they go through the panel, with a grommet.
For audio/video systems, remember that power and signal (audio/video) wiring should be routed separately to eliminate interference. If the wires need to go from the front to the rear, remove the threshold plates in the doors and route the wires in the channels most cars have there for this purpose. Finally, route your wires as far from heat sources and pinch points as possible.
Wires can chafe and short even when they aren’t routed through metal panels. Doors and windows opening and closing can cause chafing of wire bundles. There are two ways to protect against chafing on wire runs. The easiest way is to wrap your wire bundles with plastic conduit/split sleeve after you finish running it.
Wires going through a metal panel present a safety hazard, especially when they aren’t protected as they go through the panel. Movement of the wire against the panel can cause a short circuit, which can cause fuses to blow, components to fry and even fires. Grommets are the easiest way to protect wires as they penetrate panels.
One sure way to ruin an automotive electrician installation and have you wondering “What’s that smell?” is to use the wrong size, or gauge, of wire for the circuit it’s in. Using the car stereo example from above, the red main power lead is 16 gauge and has a five amp fuse in it while the main power lead for the amplifier in the trunk has a 30 amp fuse and needs a 10 gauge wire. Check out the size of the wire going to the starter; that’s a 6-0 (six-aught) wire that carries hundreds of amps to start the engine.
Although many manufacturers print circuit information on their wires, I like to make sure that I can easily and positively identify a wire at a glance. I may use colored electrical (phasing) tape to identify things like power and ground. I will also use the cable ties with a label tab to identify groups of wires (front and rear speaker channels for instance) and I will then use individual labels on the wires to identify what each goes to (left-rear negative, for instance).
Automakers have been color-coding their wires for years. I keep a good supply of wires in various colors and sizes so I can match as closely as possible the factory harness when I have splice or extend wires. This makes tracing them easier if problems arise.
When I first started doing car electrical installations, I crimped everything. I prefer to use solder and heat shrink tubing now because it holds up to vibrations better. If I have to use a crimp terminal, like when I’m connecting to the battery or a relay, I’ll apply solder to (tin) the wire before I crimp it with uninsulated terminals, melt the solder and then cover it with heat shrink.
Speaking of crimping, a special word needs to be said about crimp tools. Spend the money on a good pair. Crimps made with cheap crimpers can break the terminal/connector and/or loosen it. Quality crimpers will make safe and solid connections every time.
Carmakers like to supply power and ground to a number of circuits by connecting their power/ground leads to a single large supply wire, making dropping a gob of solder on the ball of wires, put a large staple crimp on the junction, and then wrap the hell out of it with tape. I prefer to use terminal blocks. I’ll run a large power or ground wire to the block, jump it down the terminals and then connect my circuits on the other side. They come in various sizes to accommodate wire sizes and counts (circuits) large and small and mount easily where they’re needed. Look how clean the installation is in the image above my friend Kyle did.
Image courtesy the Fab Forums
Most people think fuses when they think automotive circuit protection devices. These are great for circuits requiring 30 amps and less. However, if you’re wiring up a primary or secondary fuse panel, you’re going to need more than that. You’re going to need an automotive circuit breaker. Like a fuse, these pop open when too much current is detected. Unlike a fuse, once you fix the cause of the overcurrent, you can reset it instead of replacing it. Don’t forget fuses closer to the device being powered and relays if the device or component turns on and off with the key.
Bad grounds cause more electrical problems than anything else. The best place to get ground is the battery. As mentioned above, I like to run a big wire, like a 10 gauge, back to a terminal block and connect my devices and components to that. For those instances where I can’t do that, e.g. an amplifier, trailer connector or lights in the rear of the vehicle, I will find or drill a hole in the frame and clean it thoroughly with sandpaper or a wire wheel. Once I make my ground connection using a nut and bolt or screw (and lock washer!), I paint the area with primer to protect it against rust. An example of where someone didn’t do this and the ground failed is in the image above.
