Converting '62 Mechanical Tachometer to Electronic

I did this conversion almost 18 years ago (2002) so it is not very detailed.   Hopefully it will give you some ideas in case you are a  do-it-yourselfer.

The first requirement is to find an electronic tachometer that has the same "sweep" as the old mechanical tach.  I found an Autometer tach on ebay for $25 (sorry but I do not have the model number).  As you can see from the picture below the sweep on the old tach and the electronic tach are very close.

The next step is to dismantle both tachometers, which I will not go into.   Hopefully if you are considering this project you are capable of figuring this out.   The following two pictures show the aluminum frame that I built to support the electronic tachometer guts.

The new electronic tachometer is mounted in the old tachometer case with machine screws.  The two holes in the aluminum frame are tapped to accept the screws.   Of course this necessitates drilling two holes into the back of the old tachometer case.  The new tachometer frame was rotated so that the face will be in the proper position when these screws are tightened.

The old tach face is installed using (luckily) the same mounting holes as the new tachometer face.  It did require a little touch up paint around the screw holes.   The old needle was installed onto the new post with just a tap to seat it. This particular tachometer does not "zero" unless power is applied, so be sure that the tachometer is powered up when installing the needle.

The tachometer installed.  Note that the power is off, so the needle reads 1000 RPM.  When the switch is ON, the needle goes to zero.