rpm gauge in a mk1 golf 20v

just wondering which wire on the back of the mk1  clocks is for the rpm signal which goes to a resistor ?, also which wire is it from the ecu . agu code . is it just a sensor on the o2a gearbox for them to work

thanks alot

Mk1 clocks take a coil pulse signal to operate the rev counter, it is a negative square wave that is very noisy with high voltage spikes. Not sure what the AGU kicks out but I bet it is more like a 12v positive square wave.
On my Emerald setup I bought a small module that Emerald do that converts the ECU output to a signal the mk1 clocks expect.
I have heard of people using a diode arrangement on one of the coil drivers to simulate the tacho signal and feed that to the clocks.

i have a converter from jabba sport and was wondering how you wire it up . which wires i need from the agu ecu andthe mk1 clocks. which colour etc . and how does it reads the revs ?  thanks rob

Are you running a mk1 fuse box ?
If it is a circa 1983 one with blade fuses then there is two places you can pick up the rev counter signal going to the clocks.
Find the B connector on the back of the fuse box and pin 19, there should be a red/black wire going from there to the clocks or,
The D connector pin 15, again a red/black wire that would of come from the coil originally, connect the output of your Jabba convertor to here.

Sorry never played with an AGU module, I am sure RJ or benscab will pop up and tell which pin to use as the input to the Jabba module !

ok thanks alot and yes it is a mk1 fuse box , is there a sensor on the gearbox to count the revs /

What gearbox you using ?

Gearbox sensor is for road speed to drive the speedo.

You want engine revolutions not gearbox

its a o2a . and yes i know that ,its just i wasnt sure where the sensor comes from to read the revs or if it is already plugged in or not .

Comes off the ECU or from the pulses that are sent to the coils

rev counter is from pin 37 on ecu, runs to pin 9 of the orange 10 pin plug on the mk4 loom if its still there

ok yes so its pin 9 of the orange plug . and follow that up to the jabba sport converter then out of that to the clocks ? , do you know what colour it is from the clocks

yep you got it. the wire ya after is red/black and is to dash pin 5

and will the wire to read the revs be on the gearbx or a sensor on the engine somewhere , as i wanted to make sure its still there

Neither it comes from the ECU

ok thats great thanks alot