I did a little poking around about tach installation on the SPI motor. It seems that everyone with the SPI that installed an aftermarket tach has problems with accuracy. The reading on the tach is 1000 or more rpms off and it gets worse the higher the motor revs. You may consider selling that tach and going with a guage cluster from a manual Zetec Focus. You can have the cluster reprogrammed with the correct mileage but I think you need to get the reciept notorized or something to prove the mileage was accurate.