Re: rpm's
Check for 12-volt power and proper ground first. There may be a bad connection or a short in the wiring. A volt-ohmmeter or 12-volt test light are great tools for this procedure. When the gauge is not working, simply ground the meter or light, turn the key on and touch the positive probe to the purple wire on the back of the tach. You should see 12 volts indicated on the meter, or if you?re using a test light, its bulb should illuminate. Reverse the leads to check for proper ground, or use the ground wire on the tach to ground your meter or test light.
