Wiring isn't that prone to break with the sedan (irs) axle but you still should check it out, it's a lot more common than completely dead speedo's.

Next step will be tearing into the instrument cluster, measuring for signal presence at the back of the speedo and checking power/grounds at the cluster before replacing the speedo itself. Well, fuses of course might be the first check point :-).

If you're familiar with electronics checking the signal isn't that difficult - use a dvm set at the 2k frequency range (Hz), connect to the wiring (two pole, connections labelled s-/s+) behind the cluster, drive the car around the block and watch figures rise if the signal is present.

Forgot about this: if you go looking at under car wiring you should check the vss for continuity as well - a faulty new unit isn't that likely but of course c-o-u-l-d happen. And there btw are two different vss versions which will fit mechanically but only one will provide a working signal - report the part number back if you can.

Martin
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'65 121, '73 165