yamaha 90hp carb any good? Tach is not wired anyone familar with wires and stuff

[199675hpforce]

Guy had johnson 50hp on this boat and swapped 90hp yamaha on there. Say's boat still has johnson controls. So how can I get tach working, what makes the tach work? If I cant figure this out would putting a new yamaha controls and harness on there make sense.