I have the 2007 Dyna Service manual and it includes the complete wiring diagrams. Assuming your 2005 FXD uses the same diagram, here is the wiring info to install the factory tach.
Both the tachometer and speedometer use the same 12-place Packard connectors and the wire colors and pin locations are the same on each so you have convenient points to tap into. There are five wires to the tach.
Pin 1 - Ignition: Orange
Pin 2 - Databus: Light green/violet
Pin 5 - Battery: Brown/grey
Pin 6 - Accessory: Orange/white
pin 7 - Ground: Black.
These wires maintain the same colors back to the connector (12-place Deutsch) to the main harness, but are in different locations. There is nothing one way or the other on the existence of a tach connector nearby.
The coil wires, Blue/yellow and Orange/blue, run directly into the ECM. The light green/violet Serial Data Link (Databus) is the output from the ECM and runs to the turn signal and security modules, a data link connector, and to the instrument connector mentioned above.
One minor point to watch for is the black ground wires on the speedo connector. Don't tap into the black wires from pins 8 or 11, these go to the trip reset switch only and do not appear to be an actual system ground.
Hope this helps. Let us know when you get the tach connected.