Went to ride 2007 Dyna. The key was out but the tachometer was quietly clicking and bouncing near 2700. I'm sure it wasn't doing this when I parked it. I disconnected the battery and needle stayed at 2700. I took tach out and disconnected and it's stuck at 2700. What do you think happened after I parked it? Is the tach bad or is it a wiring issue that I need to trace? Where do I begin?

 

You didn't say what model you have. Some had tachs, others didn't.
Simple stuff first. Start by cleaning and tightening both ends of both battery cables. If no change, then start with the wiring to the back side of the gauge. Trace it to the end, which should be at the fuse/relay box. Check for blown fuses. Any corrosion on the contacts for the fuses and relays must be cleaned up. Using dielectric grease on the contacts is a good idea.

 

Your tach is electronic, the needle is moved by electrical components and not free to move on it's own. As stated in the earlier post start with the basics on cleaning electrical connections both hot and ground.