You need to make sure the relative markings on the scale are the same for each gauge, otherwise your DIY conversion is a non-starter (if you want an
accurate rev counter). Is the red line the same number of degrees round the scale from zero in both gauges?
If in any doubt, these guys
http://www.jdo1.com/index.html will
convert any rev counter to electronic operation at a reasonable price.
IF the rev counter is like the speedo, you need to "preset" the tension on the needle spring, so that the spring holds the needle against the zero stop
with a certain force. From what I recall, there should be two little white dots just beyond the arc of the needle, and on the "negative" side of zero.
You place the needle on the spindle with the spring fully "relaxed" and the needle pointer lined up with these two dots, so that when you rotate the
needle clockwise and beyond the zero stop, there is the correct tension on the needle at zero. This certainly applies to speedos and I would expect it
to apply to mechanical rev counters. May not be necessary on electronic ones, but if there are two little dots below zero, it might be worth seeing if
that is where the needle naturally ends up if the zero stop pin is removed or overcome.
Can't recall how you get the pointer over the zero stop pin. You may be able to press the needle only part way onto the spindle, or flex the needle
over the top of the stop pin. In the factory the stop pin was probably fitted last, but I would be a little reluctant to try taking out the stop pin.
Might work though as you could superglue it in again afterwards. But DON'T be tempted to bend the stop pin as that will almost certainly flake the
paint off the surface of the dial which is the very thing you are trying to keep.
If this is the case on your dials, just remember to use the correct setting point for the ELECTRONIC rev counter needle, not the Jaeger setting marks
as it's the internals of the rev counter you are trying to match up.