Yup, that's limp mode, take it easy till the speedo is fixed then re-set the computer.

Did you check to make sure the plug on the box is ok? haven't ripped the wires out?

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Beaten up old 98 Gen 2 Liberty, 13.0, stock V3 STI running gear.
07 Transit motor home
69 VF & 70 VG Valiants needing full restoration
Yamaha Zooma 50cc rocket hopefully going with the Transit.