Thanks for the reply - I'm pretty sure the tacho signal needs some sort of suppressor to make it work properly. The signal is making it read correctly, it just flickers. On the other hand, omex has a tacho output that may work, although the pin is missing from the plug.. might be able to get one from omex

As there's no haynes for a 1.7 puma, trying to wire this temp gauge is proving difficult. You're right in that the ecu puts out to the clocks. There must be a way of making it work. Omex doesn't output a signal.