How to Install a Tachometer: 8 Steps (with Pictures) - wikiHow May 15, 2011How to Install a Tachometer. A tachometer is used to indicate the revolutions per minute (RPM) being performed by a car engine. Most cars with automatic transmissions are not equipped with a tachometer, since a tachometer is mostly used to..51%(232)Views: 227K Tachometer Repair Restotation for Mustang Classic Cars 1965 mustang rally pac tachometer and clock restored, tachometers updated to 3 wire, no decals or stickers accurate and reliable, 65 mustang tachometer upgraded to 3 wire! 6 year warranty. also, with the 3 wire conversion, you never have to worry about the transformer going out in your original ford electronic circuit.