No, they didn't come with faulty wiring, its that with age, the wires and the contacts get a thin layer of corrosion on them. The contact point at a connection is decreased and the amperage going through the smaller connection builds resistance which turns into heat.
Pull the plug on the light switch and view both side of the larger red wire going into it. Check the black plastic around that wire to see if its melted or burnt. If not, pull the switch and inspect the dimmer ring and contacts. If nothing else, take some sandpaper and scuff the contacts of the switch and use some grease to protect them from moisture.
Oh, and carry a fire extinguisher if you don't have one.
1975 CJ-6 1983 CJ-8
1986 CJ-7 Laredo 1986 TJ-7 Trail Jeep
2003 Inca Gold TJ Rubicon