Rev counter trigger location

[Orangecab]

Hi, haven't been on here in about 6 months and haven't touched my car in about as long!

What I'm after if anybody knows is where does the Rev counter on a 6 pot get its trigger from? As I will be fitting a non Bmw engine and wanted to know if I'd need to make a trigger on the crank pulley etc

Tia rob

[gromgsxr]

on the later cars the tacho is driven by the stock ecu, its a 12v square wave signal one pulse per ignition event.

[Orangecab]

What about the early model? As I can change bits and bobs around to suit, any idea how to make the Rev counter work on a v8 carb engine to e30 clocks, either early or late clocks as I assume they are interchangeable!