if there is an error, the vehicle parking lights will flash, count the number of times it flashes and there is an error table.
it sounds like a common thing with these, if they used virtual tach instead of actually hard wiring the tach signal wire then that might be why. virtual tach isn't "bad" persay, but it's not refined enough yet imo. I'd just go in there and ask if they wired the tach wire or used virtual tach. if they used virtual tach, tell them you rather have the tach wire connected instead.