TheFlyingPolak wrote:That's right, an electronic RPM counter, takes pulses directly from the ignition
If the tacho is any thing like the later Saxon Models ( and I'm pretty sure the wiring is similar ) or any MZ with electronic tacho then as far as I can see the pulses derive from the
unrectified output of the alternator, not the ignition system. This is easier and safer. The alternator thus provides an
AC trigger voltage /signal to the
S terminal of the unit which is directly Frequency vs Rev related. The other 2x connections are just Negative and Positive supply. Knowing this makes fault finding easier.
1) First check with a
DC voltmeter (multi-meter) that you have the full battery voltage at the + and
- terminals at the tacho when the ignition is switched on.
2) Then remove the
S wire from the unit. Set your meter to
AC VOLTS around the 30 volt range and connect the test leads (anyway round) to the
S wire and
ground. You should see a voltage (I would suspect around 12-20 volts) depending on how much you rev the engine. Stopping the engine should see the reading go down to ZERO.
3) Note if you have a better meter which has
frequency in Hz you can then select this setting and see for yourself the frequency rise as you rev the engine.
Doing the above test will at least give you confidence that you are not wasting your money by trying to source another tacho as it will check the wiring needed to drive the tacho.
These tests will take only a few minutes so worth doing....Les