Best type of wire to connect an original Lionel TMCC Command Base to the track.

Any wire will do, solid/stranded/18-16-14Ga. Shortest length to connect to the "U" post on transformer.

Yes, connect to the transformer U Post (as said above).  Any gauge 14-16-18 will work.

22 or 24 AWG will work as well. There is little current involved here.

Pete

Right now my Legacy is connected using a #28 wire, works fine.  No current of consequence is flowing in the wire.

Thanks Paul RT John and Pete for your replies. I've been using the same wire for years and thought I's ask if anyone had a preference.

It is a very important wire to connect and stay connected. I would use stranded wire with crimped and soldered connectors on both ends. 

Norton posted:22 or 24 AWG will work as well. There is little current involved here.

Pete

That's true.  So very true.

I always do more than necessary with electricity or electronics.

Thanks all for your comments.