The handy shop tool for testing tachometers

 Every workshop needs one of these....  a simple tester to determine if a tachometer is functional and reasonably accurate. It may surprise you, but many older analog tachometers are inaccurate and this little tool will quickly expose them for what they are! 

TACH-TEST is simple to use.  Just connect it to a 12V source (for example, the vehicle battery) and connect the 3 other leads (power ground and signal) to your tachometer. Very useful for checking functionality and accuracy of the tachometer as well as troubleshooting signal continuity through the vehicle wiring to the tach.    Switch selectable, this unit works with most 4, 6 and 8-cylinder tachs. For rpms, the rotary switch selects zero, 500, and 1000 to 10000 rpm in 1K steps with an accuracy of a few %.  An output switch lets you choose between a low and high-level trigger signal. An LED indicates output activity.  The unit comes with 3-foot power cord and output leads with insulated alligator clips to make attachment to 12V power and the Tach quick and easy. The output "LO" position, provides a current limited 12V rectangular wave signal to the tach.  In the "HI" position that signal is enhanced with a 150V 'spike' to trigger older high-voltage tachs that were connected to the points/coil signal.   These low-energy signals will not damage your tach. Unit is reverse-battery protected and short-circuit protected.