Wiring SimplicityThe Retrogauge Mini-Tach is easy to wire. There are three leads: Signal, 12-volts, and Ground. Signal goes to the "-" or distributor side of the ignition coil. The 12-volt power lead should be switched power, meaning it's live only with the ignition switch on. Ground, as its name implies, grounds to the body. We suggest making a mini-harness to support the Mini-Tach. Wrap it into plastic conduit or with electrical tape to make sure everything is secure. Route the signal lead through a rubber grommet located in the firewall, ideally where your Mustang's air conditioning compressor clutch lead goes or through one of the vacuum-hose passages. Don't drill a hole in the firewall unless there's no other option. Always drill where the factory did, which can be identified as a dimple mark in the firewall.
Preventative MaintenanceWhile you have the instrument panel out, take care of the speedometer cable and head with the all-important lubrication. Based on years of experience, we suggest a mix of white grease and WD-40, which keeps the speedometer cable lubricated even in the coldest of weather. Draw the cable out, fill your hand with white grease and WD-40, then run the cable through the mix.
Consider replacing the instrument voltage regulator and light bulbs while you're at it. The instrument voltage regulator, or voltage limiter, regulates instrument power to ground to maintain constant instrument voltage. When it fails, instruments won't work at all or they will peg out at maximum. In either case, replace the voltage limiter.