Blew up Autometer Electric Speedo

[Northern Goat]

In the process of doing an LS conversion and added a full set of Ultra Lite electric gauges. Hooked up power, ground and speed sensor wires (no signal from ECU as the ECU was no installed).
Day 1 and all is good. Gauges all sweep and Speedo shows 2 km. Continue to check all other electrical items run from the dash and all is good.
Day 2 everything works except the Speedo. No sweep, no odometer only backlighting works. Even jacked up the car and ran it but o speed signal.
Called Autometer and they say it’s my fault even though they cannot tell me what I did wrong.
Now obviously not happy about having to shell out to buy a new Speedo, but I’m more concerned about what could have gone wrong so I don’t blow another gauge up.
Any ideas would be greatly appreciated.