Tach Not Working

A simple test is to test the IDM circuit for continuity. You will need a DVM and know how to use it for measuring resistance. Measure the resistance between the tan/yellow wire on the TFI module connector and the tan/yellow wire on the instrument cluster connector. You should see 22K Ohms (22,000) +/- 10%. More or less resistance beyond the 10% tolerance means that the resistor has gone bad.

See http://www.stangnet.com/tech/cluster87-93.pdf for a pinout of the instrument cluster.

Diagrams courtesy of Tmoss & Stang&2birds
Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs



There are procedures to test the tach, but you need a audio frequency signal generator and frequency counter to do them. This is out of the range of expertise for most people here on Stangnet.

I had the same problem if you pull the gauge cluster out and look at the back the tach comes out separate of the cluster shine a light to the face of it and the 3 little resistors are on the corner if you see burn marks near them just resolder them and it will work fine this happens quite a bit I. These I have had two already