I am having trouble with my smiths tacho.
Its on my rover 4.6 running with a bosch motronic ecu.
I have followed the wiring diagram, used the b/w wire instead of the r/blue wire but it still does not indicate actual revs ( from diagnostic thingy and my phone)
Now after some research it may be that the output from the ecu is not 'right' for the tacho.
There is another wire on the tacho which is 'Pull up for open collector ecu output'
I cannot find any info on how to use this wire - where and how to connect it.

Is the bosch motronc giving an ' open collector' output? I can't find any info this either

Any info gratefully received