Hi the Weller gun pictured below works great you also need solder flix and clean the track thoroughly or solder won't stick use a Weller gun on second press button for highest heart run the copper iron tip back and forth rubbing the side of the track while heating and keep solder flux and solder until solder stick the attach the wire you need and solder hold wire firmly and let cool or you'll have a cold solder joint !
Weller D550 Dual Heat Professional Soldering Gun - Weller Soldering Iron - Amazon.com
How to solder wires onto Lionel track - Bing video
Alan