If it's like the AE92 (I'm assuming it is) then the speedo cable will run out from the firewall into the gearbox (somewhat thick and firm cable). It should have a screw-on join about halfway along, unscrew that and the end on the gearbox and check it's not broken. It's not uncommon for the speedo cable to break on the lower section due to a lack of grease (they are designed to spin the grease up the cable so can dry up below).
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