I bought a $7 special from JCWhitney, just as an afterthought when ordering some other parts. Maybe weatherstrips for the doors? I mounted it to the top of the steering column between the gas gauge/idiot lights and the speedometer. It covers the brake warning light, but the truck won't hardly move if the brake is on, so I don't care.
I used a couple tie-wraps, head to tail, wrapped around the column rather than trying to drill into the plastic, and it seems to pretty much stay. It is just about as visible as the speedo, etc. Under dash would not be in my sightline, and on-dash just didn't seem normal to me as I'm too old to be a 'racer', and don't need a tach proudly displayed for my old non-performance 4-banger.
tom