Anybody thought about using a GPS Speedometer? I think that's the route I'm going.
They're a little pricey, but 100% accurate, and
no cables or sensors to worry about.
Just a power wire and you're good to go.
http://www.speedhut.com/gauges/GPS-S...KtMaAmow8P8HAQ
They've even got odometer and trip odometer too.
To me, it's worth it to not have to worry about getting an accurate speedo hooked up.
They do have an external antenna but I assume it would be just like a GPS in your car, just set it on the dash.