Well, they are known to snap internally, especially if you have an M40 cable and an M41 gearbox.

The easiest way to check that it is indeed hooked up would be to crawl under the car and look for the long cable with a wire spring wrap that should be screwed into the side of the gearbox near the main output shaft.

The other end of that cable crawls up the firewall and enters where your two carburater choke cable come in. It should be screwed into the side of the instrument panel up under the dash.

If it is hooked up, but you have no speedo, then it either snapped internally (and is cheap enough to replace from Skandix or SwedishTreasures) or the plastic speedometer gear inside the gearbox broke/melted/failed in some way. The later is a bit more trouble to replace. I've experienced both failures.

It is also possible that the instrument cluster failed... But frankly I've *never* seen or heard of that happening. The odometer gear is prone to failure and I've also had to replace the odometer gear.