So assuming you have a separate voltage regulator, more or less stock wiring and an ammeter..............assuming alternator is wired properly to regulator and etc.
1. Black Wire from ammeter pos to 6 pin connector. Thru connector to starter solenoid "B" (battery) terminal.
2. BLK with WHT stripe wire from ammeter neg to 9 pin connector. Thru connector to horn relay Battery terminal/screw. The horn relay does double duty as a power distribution point/junction block, whatever you want to call it.
Not sure about original wire colors since you are switching clusters, and not sure if they have been changed by PO, so wire per above regardless if colors match.
If no change in issue after answering questions and wiring per above, we will begin trouble shooting if you wish.
