Installing an aftermarket tachometer

[kiii]

Hi!

I have an old Mk3, with the 2 clock dash fascia (no stock tachometer)
I bought a standard aftermarket tachometer as I thought it'll be a super easy fit (first mistake i guess)
Wired up the ground, 12V ignition, and a wire to the neg of the ignition coil as needed

Tachometer isn't moving past zero. It definitely works as it does a full range sweep as soon as the ignition is on, and it's new out the box.

It looks like the wire from the neg of the ignition coil is pulling between 0.1 - 0.5V AC depending on the revs.
Looks like my tachometer wants more power from source (i'm assuming around 5V is standard (there is no manual with the tach, and info online is a bit scatty)

Is there a way to 'increase the volts from the ignition coil' for the tach, or does anyone know of any tachs that would work on the car at that voltage

Thanks!

[stevemarl]

If you`re getting 0.1v at the points I assume that`s just the voltage drop ACROSS the points themselves due to the small resistance. You need to test the DC voltages as you turn the engine by hand through a closed/open points. Tacho`s are not normally a problem, is it a normal points ignition, no electronics?