Tachometer only works while cranking

[stang_380]

Since i have relocated all my wiring behind the fenders and dash my factory tachometer will only move (appear to work) while im cranking the starter. After running the tach just reads 0. I have a MSD-6AL also. What did I miss here?

Thanks again for all the help here on the Stangnet,

Erik

 

[jrichker]

The tach picks up its signal from the IDM line on the TFI. It is a Dark green/yellow wire that connects to pin 22 on the computer. There is a 22K ohm resistor between the TFI and pin 4 on the computer. You may have broken the wiring between the computer and TFI, in which case you would get a code and the stock tach will not work

Code 16 - Electronic ignition - IDM circuit fault - Ignition Systems. Bad wiring, possible bad TFI. The computer isn’t seeing the proper IDM signal coming from the TFI circuit. There is a 22,000 ohm resistor in the dark green/ yellow wire that goes to pin 4 on the computer. Disconnect the TFI connector and remove the passenger side kick panel. Then loosen the 10 MM bolt to disconnect the computer connector. Use an ohmmeter to measure the resistance between pin 4 and the dark green/ yellow wire on the TFI connector. You should see 21 - 23 K ohms (21,000-23,000 ohms). If not the dark green/ yellow wire is broken or has a bad connection. If this checks out OK, measure between the dark green/ yellow wire and ground. You should see 1 M Ohm or more, OR an infinite reading. Less that 100 K ohms means a short to ground somewhere in the dark green/ yellow wire.

 

[stang_380]

Thanks for the response. Im going to look into this tonight. Just a thought though... While I was doing the whole wiring project I removed the bulb for the airbag warning light in the cluster. Is there any sort of relationship with removing the bulb and my tach not working?

 

[jrichker]

Thanks for the response. Im going to look into this tonight. Just a thought though... While I was doing the whole wiring project I removed the bulb for the airbag warning light in the cluster. Is there any sort of relationship with removing the bulb and my tach not working?

No connection between the two systems. You may have shaken loose some of the connections to the instrument cluster if you removed it.