Excessive heat is usually a sign of resistance somewhere in the cable, or in the connection. It is very possible that the cables look good but are internally corroded. This happened to me and it actually blew the top post off of a battery
I don't think that it is necessary to upgraded the F/R switch. It is more important that you get the correct F/R switch for your cart, and then check or change all of the cables in question. If you're not sure of the cable condition, change them all. Now's a good time to go to 4 gauge cables if they are 6 gauge.