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Conversion to Tachs
Before the 1967 model year, tachometers were added to Mustangs via the Rally Pac system. No change to the underdash harness is required for 1964.5 to 1966 model years.
For 1967 and 1968 models, we perform the conversion from non-tach (standard) to tach conversions so that the wiring and plug configurations are identical in functionality with the OEM's original designs. Unfortunately, there is no public domain wiring schematics for the tach harnesses, so we reverse-engineered them. We guarantee that these harnesses perform identically with the OEM's specifications. The 1967 and 1968 harnesses also require changes to the underdash to dash cluster sub-harnesses. The headlamp and alternator harnesses must also be replaced, and can be obtained with reproduction parts.
For 1969 and 1970 models, wiring schematics are publicly available. Surprisingly, every website that claims to offer conversion strategies do not conform to the OEM design, leaving the ammeter (unfused) lines in place and ignore the alternator dash lamp system. We remove the ammeter lines both at the firewall connector and at the dash cluster, isolating those wires completely. For the alternator lamp system, a resistor wire is required for proper operation which we add. As with earlier models, both the headlamp and alternator harnesses in the engine compartment must be replaced with tach versions. Finally, the circuit board on the dash cluster (as well as the dash cluster!) must be replaced.
For 1971 to 1973 models, the wiring schematics are available, but difficult to decipher. Further, the dash cluster connector changes configuration and size from non-tach to tach configuration. As usual, all the engine related wiring must be changed out, as well as the dash cluster and printed circuit card. The engine side harnesses are not yet available in reproduction.