Has anyone ever tapped into the speed signal that comes for the dash? I've read that it can be done but have never heard of anyone actually doing it. I'd like to setup gear based boost trims over Christmas vacation.

 

I'm interested in doing the same thing. The issue is which, if any, 1.6 Miatas have this output. I suspect that mine, which had the MSSS stereo, does (the stereo would adjust bass output based on road speed). I haven't investigated yet, but here are a couple of posts with useful info:
MX-5 Miata Forum - View Single Post - Improving traction.
MX-5 Miata Forum - View Single Post - Improving traction.

 

I found this link, which I'll investigate once the car is on the road again:
http://miata.fosketts.net/index.php?...22ALC.22_do.3F