Quick Tech: Ten Tips To Make Wiring An Aftermarket Dash Easier

Limiting the movement of wires through the use of zip-ties is highly recommended. It looks neater, too.

Many enthusiasts have no compulsion about grabbing some wrenches and replacing the hard parts in their rides like carburetors, camshafts, ignitions, and headers to name a few. But for all things electrical, quite often there’s a bit of apprehension before tackling a project.

One of the more daunting tasks —in the eyes of many— is replacing the OEM instrument panel with a contemporary digital or analog system. But it’s actually a fairly straightforward affair. So for some professional input, we turned to the folks at Classic Dash in Carson City, Nevada — who have worked with customers on their installation issues for some 20+ years.

1. Organize Everything
It sounds pretty basic, but having all the necessary tools, wires, and components laid out before tackling a project saves time in the long run. Make sure everything is readily at hand.

2. Read The Instructions
Some folks get tripped up with the “I’ve always done it this way before” syndrome as things can change procedurally, in component specifications and safeguards. General and application-specific instructions are available online at www.ClassicDash.com.

The recommended method of connecting two wires includes stripping both ends, twisting them together, soldering the connection, and protecting it with a heat-shrink shield.

3. Trial Fit The Components
Because some vehicles are manufactured in multiple facilities there can be differences from one car or truck to the next. Some dash panels, for example, may need to be trimmed slightly —or the host vehicle modified to assure a perfect fit.

4. Proper I.D. Is Important
Before removing any factory gauges take care to identify each wire that runs to it. A roll of 1/2-inch masking tape and a Sharpie (or pen) are commonly employed. This will prevent much aggravation.

5. The Ohms Have It
A common problem is mismatching the resistance of the fuel tank sending unit with the gauge. There are over a half-dozen possibilities. For example, pre-1965 GM vehicles range from 0 ohms (empty) to 30 ohms (full). Later GM cars are 0-90, and there are differences between Ford and Chrysler, cars and trucks. For this reason, Classic Dash supplies an application-specific gauge to match the OEM sender. For those with aftermarket or auxiliary fuel tanks, you can measure the tank unit using an Ohm meter and noting the resistance as you move the lever. The fuel level gauge Ohm range must correspond with the tank sender.

6. Resistance Is A Factor
There’s a definite correlation between the thickness (and length) of a wire and the amount of resistance encountered. A 14-gauge wire (0.064-inch core diameter) offers about 1/4 the resistance of a 20-gauge wire (0.032-inch). The wires in a Classic Dash loom are all 18-gauge and offer excellent conductivity. Using a smaller wire is asking for trouble. Of course, you’ll want to use heavy-gauge wire for tasks that see high levels of current like ignition systems, starters, etc. This is dependent on amperage and the length of the wire. Respected starter/alternator manufacturer PowerMaster offers the following guidelines.

Here’s a typical wiring harness for analog gauge installations.

7. Connections Are Critical
The no. 1 cause of problems in wiring is improper wire-to-wire connections. Yes, crimp-type connectors can do the job. But total reliability is assured when you follow it up with solder or simply weave the two strands together and solder it. Classic Dash highly recommends it.

8. Tie-wraps Are Your Friend
It’s important to prevent wires from moving around, as this can lead to wire fatigue and breaking of the strands. Not only does it look neat to secure and bundle up loose wires, but it’s good to anchor them to something stationary.

Aftermarket gauges come with specially calibrated sending units. Replace the OEM sending units with the new ones.

9. Ditch The OEM Sending Units
All gauge packages from Classic Dash and other manufacturers come with temperature and pressure sending units that are calibrated for use with their specific gauges. Using the stock unit, of a different aftermarket brand, can likely lead to erroneous readings.

10. Optimize Signal Strength
As you might suspect, GPS speedometers depend on getting satellite signals. Care must be taken in mounting the antenna in such a manner that it’s clear of interference. Mounting it on top of the dash is optimal. Classic Dash offers special GPS speedometer modules for the task.

Article Sources

About the author

Bill Holland

Bill Holland has been involved in racing and the performance aftermarket since the 1960s in the capacities of racer, speed shop proprietor, journalist, street rodder, designer and advertising/PR/marketing professional. Along the way he’s raced Top Fuel and Funny Car, been editor of NHRA’s publication, National Dragster, was involved in off-roading as publisher of SCORE News, built a variety of Featured Vehicles for the SEMA Show, as well as a Track “T” that was a Contender for the AMBR award. He currently races vintage sports cars. Bill was inducted into NHRA’s California Hot Rod Reunion Hall of Fame in 2017.
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