i put new motors in and they worked good until the ground wire, in the switch started smoking badly. i d understand the hot, but the ground?

 

the ground completes the circuit... if you have 15 amps flowing thru the hot, you have at least, 15 amps flowing thru the devices ground (more if it is shared by something else.
also, if one of the connectors has let a little resistance build up, from corosion, or the wire is loose, then heat will build up and cause the wire to smoke... doesn't matter where.
if the wire is getting hot in one spot... that is where your resistance is it means bad connection, corrosion, or break in the wire (even a partial break in the wire )
if the insulation is already burned, you'll have to replace it. watch out if it's at the connection of the switch, the heat could get up into the switch (even a new switch) and weaken it.
I've seen connections get hot enough to cause solder to melt and run out of the connectiion (water had leaked in an caused corrosion).
sounds like you need to buy a new/used connector pigtail.