QuestionQUESTION: My tachometer has not worked for several years. It has an Allison ignition module installed 20 years ago. I know the tach previously worked. I have a Haynes manual with wiring diagrams. The car drives fine, but I'd like to get the tach working again.
To start with, how do I bench test the tach gauge to determine if it's still good? (w/o blowing it up, which is why I'm asking).
The back of the Smiths gauge has one round post, one blade connector next to the round post, and one blade connector on the gauge body (the ground?). The wiring diagram doesn't help because of the Allison unit. Also the diagram shows a line from the tach to the voltage regulator which I don't know what it looks like to find it, so is that it's "hot" power source for the tach?
ANSWER: Hi Mike,
No bench test that I know of, so I always have to do the tests on the car. I need to look at a wiring diagram of your car so you need to tell me what year 1500 it is.
Howard
---------- FOLLOW-UP ----------
QUESTION: Howard, sorry for the late reply. The AllExperts email got put in my auto-Spam folder. When I didn't see a reply for a while, I checked the Spam folder and there it was. To answer, my Spitfire 1500 was made in 1975, it's original Comm.# is in the 28000 range. Thank you for your time. I do appreciate it. Cheers, Mike
AnswerHi Mike,
Your tach only has three connections. A ground on the case, a spade connector the picks up the ignition pulse signal from the negative side of the coil and a power wire that picks up it's power supply from the power side of the instrument voltage stabilizer. (not the voltage regulator which is in the alternator)
If it is receiving the ignition pulse signal and has power from the stabilizer and is grounded. And does not operate then the tach is bad.
Howard
