Quoted from GLSP3022:A member of the Taxi club says some LED displays are wired incorrectly and do not allow the game to work properly unless you hack the boards...
Unless aforementioned member can provide specific details on said wiring issue and the fix I'd guess that's BS. If it's legit some searching on Pinside or Pinwiki should turn up some info.
Pinwiki does mention the lane change switches are problematic. I see some troubleshooting in your future.