Im still having trouble getting my rev counter to work on my Saff coss. I purchased the car with it not working and have now replaced the clocks and tried another ECU and it still doesn’t work...

It could be the wiring in-between i guess but im running out of ideas, where does the ECU get the rev information? Also if the ECU didn’t know what revs the engine was doing i guess the engine wouldn’t run, or badly anyway?

Cheers for any help