I got this 1987 240 free from a guy that had taken out the dash to replace the fan motor. He finished the job but I think he made a mistake wiring up the cluster upon replacement. He has the orange wire plugged into the spot with two male spade connections and he also plugged the white/red stripe on the other open male spade in that location.

My understanding is that the white/red stripe wire is for an optional tach. This car has none so that wire should be a spare wire taped off.
Studying this issue, on this forum, I've read that this is a common mistake and it renders the Speedo worthless.
1) Is my understanding of this blunder correct?
2) If so, do I have to replace the whole instrument cluster or is there a board that needs replacing?
3) will this wiring blunder affect the charging system ( having issues with charging too but one thing at a time)?

Thanks in advance,
Gus