Recently installed an Autometer Pro Cycle 2 5/8" Tach and H-D #68961-98A CHROME BILLET MINI TACH MOUNT on my '05 Road King.
Don't know your mechanical abilities, but it wasn't too difficult to install.
Using the factory Service Manual along with the necessary wire terminals, I installed the wiring along the factory harness and plugged directly into the fuse block and speedometer connector. Grounded to one of the two factory studs in front of battery. Very clean installation, and the Tach works flawlessly.