Have you checked for a voltage rise when motor is running ?
if no voltage rise it could be a blown rectifier.
I had this on mine and thought it was bad wiring, as soon as I saw it was not charging it fell into place.
no charge then no tacho .
just a thought.
also what can happen is a break in yellow and orange wires (mainly yellow) under the flywheel, I also suffered with this..
the wire is wrapped up nice and tight and then bent to go under the flywheel.
where over the years the wrapping gets a touch weak the wires touch on the flywheel and get broken/cut.
this was on a oval port but I have heard same things have happened to bridgeports.
Mine had the stator wires broke on both my engines, 1 was nice and easy to repair the other a pain the arse.
They get broke so close to the stator but you can repair with a bit of patience and lots of swearing.
A bit of solder and some epoxy resin and a bit of tape for good measure does a decent repair.
here is a couple of pics of stator wires that I found cut through.
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hopefully yours is not like this, but if its not the rectifier then this is the next place to check.
2 different stators but same symptoms.
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