So my factory tachs in both amx's did not work. I ended up buying a sun brand tach(the sweep is very close to the same) and used its new guts using the original amc face plate
I mocked up the new circuit board and two new screws into the old face plate to hold it. I took the original tach hand and cut just the white pointer off. Cut the new tachs orange pointer off and re glue the original on to the new tach base. The hole size was different.
old vs new pointer
new board on old face plate
old pointed glued to new base
When installing add 12v power so you can put the needle on the 0 rpm
Clean tach face done vs how yellowed the speedometer was. Used normal car wax and some elbow grease