Tach Not Working

[CMArnold51]

I have a 1992 lx 5.0 and cant seem to figure out the in dash tach. The previous owner put a different steering column in the car, however when he pulled the dash he screwed up the tach.. my tach only wprks after 4k rpm and always says 4k rpm even on idle which I know is wrong. . Any one got any advice?? Thanks

 

[jrichker]

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.

 

[Mellostang]

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