Ok, so in the three weeks I've owned my '90 F-250, the tach has worked twice. Once in the morning after it rained all night, and today after my car wash, well, it turned on in the middle of my car wash.

This seems odd to me, and makes me think the tach isn't dead?

 

Moisture completing the circuit?

 

What would that mean in terms of fixing it?

 

Most likely the sensor as stated before ... If the wires are cracked or loose in the plastic where they enter the sensor then that raises the probability.

I personally have never seen any other tach failure!
That does not mean other failures do not occur.

-Enjoy
fh : )_~

 

Ok! I'll order the new sensor tomorrow(: just making sure, because I found this very strange