[AirSpeed]

When I was about 16 (decades ago) I helped a guy make a speedometer for an old Datsun pickup, we used some magnets and a pickup out of one of those aftermarket cruise control kits from JC Whitney, the magnets mounted on the driveshaft and the pickup was mounted on the underside of the truck next to the driveline magnet. We ran the wire from the pickup up to a cheap tachometer mounted on the dash. To calibrate it I drove behind him and flashed my lights at a few speeds we had worked out earlier and marked the tack at those speeds. we had to add a couple magnets to get the tach to move, one wouldn't give enough signal to move the tach far enough.
I am not positive why we did this instead of repairing the original speedo system, it was a long time ago! I do remember it worked really good though.
If a couple of baked teenagers can figure it out how to make it work I bet a grown up adult could adapt something like this into a stock dash!
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