What makes the tach work?
 

I'm having a running rich problem with my 3.2 carrera and I was wondering about the two timing/speed sensors.

I'm thinking my sensors are OK as the tach seems to work fine.

The dizzy is mechanically linked to the engine but as we know it doesn't have any electronics inside it.

I'm guessing that it's either a signal for the tdc sensor or the speed sensor?
Does anyone know which?

I've read the speed sensor allows the fuel pumps to come. Does it have any other function?

TIA.