If it's noticeably warm it's most likely a high contact resistance somewhere in the circuit. Cumulative high contact resistances from age and corrosion can cause all sorts of gremlins to pop up. A thorough cleaning of all electrical contact points with contact cleaner and coating with dielectric grease is always recommended basic maintenance, grounds, bullet connectors, plugs, switches, fuse boxes, etc. I always put star washers on both sides of my grounds so they dig in real good and maintain contact. Bad grounds are often overlooked and I don't consider frame grounds and associated bolted together parts a brilliant design. I always run a ground from my battery to a R/R bolt or near by and spider out to all parts of the bike from there. FYI, switch maintenance is always recommended in a nice clear plastic bag so springs and small contacts don't get lost.