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Reliable Dash & Instrument Wiring

Posted in How To: Electrical on November 9, 2017
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Last month, we covered some tips on layout and populating a dash with gauges, switches, and other controls, whether it be adding to an existing vehicle panel or building a dash from scratch. Following that type of work is the wiring of the instrumentation and electrical components. Given that your vehicle is subjected to the extremes of temperature, vibration, dust, and humidity, it makes sense that electrical wiring deserves careful attention if you want to ensure its reliable function under those conditions for a long period of time.

When choosing components and before you start wiring, there are a few decisions to make, such as whether to use solder joints or mechanical terminal connections. When wiring a dash or other panel you might consider a master connector or multiple connectors that allow you to easily remove it in the future. However, note that connectors are one of the weakest wiring locations in a vehicle.

It should be common knowledge that wire size choice should be based on current draw of the circuit, and proper fusing of the positive power wire near its source is a good idea. Consider also any mechanical factors than can affect your wiring such as how it's routed, if there are any abrasion or heat hazards, and other movement issues that should be addressed since the vehicle will be shaking the wiring the whole time it's in use.

You can purchase switches with several types of terminals: screw, push-on blade, or solder pin. Soldering means you’re not relying solely on a tightened mechanical connection and can be more reliable. However, the other terminal types can work well with attention to connection tightness, and they have the ability to be quickly removed if needed.
If you decide to use crimped connectors when wiring, consider avoiding the cheap pliers-type crimpers you see in most inexpensive kits. A jaw-type crimper, or similar, designed to work with the crimp connectors you're using will produce a higher quality and more reliable mechanical crimp.
Connectors can be purchased with or without plastic insulation. When soldering terminals, the plastic can be removed from the insulated variety. Once the solder joint is complete, it can be covered with heat-shrink tubing. Adhesive-lined shrink tubing with a higher shrink rate (about 3:1) helps seal joints well and stays in place reliably.
Doing a clean layout of your wiring helps avoid mistakes, and it looks great too. Consider where you're headed with each wire and some can be daisy-chained to save wire and clutter if the wire current rating isn’t exceeded. When doing automotive wiring, consider the stress of bouncing and vibration on the wiring. Allow some slack for slight movement where needed, but support longer runs so they don't move around and risk fatiguing the connections. Staking can be done with loop clamps and/or or zip-ties.
Any time you need to feed a large power cable through the firewall or other panel, you can simply use a good-sized hole with a grommet for insulation protection. However, a cleaner means of crossing power through a metal panel is using a stud-type, feed-through junction block. It can be mounted to your panel with a couple of screws and provides a safe way to attach power wires to both sides of the panel. They're available in multiple sizes and current ratings.
We've used these ground junction blocks salvaged from GM vehicles. One can be secured to body metal ground with a single bolt and provide multiple ground wires that can be routed to various locations as needed. Remember that electrical current must operate in a complete loop, so a poor ground connection or loss of ground can cause just as many issues as a problematic power feed wire.

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