E30 Zone

hi guys was just wondering if anyone knows where the signal for the rev counter is picked up from got a fault where my speedo is not working i have been told it recieves its signal from the crank sensor but these were replaced not long ago when it had a different fault which turned out to be an ecu fault which was repaired. i do not have any voltage from pin 21 on the ecu which is the speedo wire. car is a c reg m20 b25 pre facelift. any help is much appriciated many thanks.

so is your problem with the speedo or tachometer?

if its speedo then 99% of the time it is the wires broken to the sensor mouted on the diff.
Speedo and tacho are basically unrelated.

however in the interst of answering your question the instrument cluster gets the engine speed from the ECU, and if memeory serves me correct its pin 74.

its the tachometer i've traced the wire all the way back to the ecu and according to the wiring diagram its pin 21 and thats wot i have got don't forget its got an early type ecu? How does the ecu get the engine speed though through a crank sensor or somewhere else?

take it that no ones got a clue then well back to the drawering board lol.