Agree with Jagiven about the potential switch problem, but the burned covers is also a concern. If all the covers are burned, something is getting too hot. Do you have all fuses, or is there a breaker in the circuit somewhere ? I have had a situation in my house where the breaker did not blow, and wires got hot enough to blacken the insulation. Later we found a mouse had gotten in the wall and chewed the insulation just enough to cause a mini-short which did not blow the breaker. You might want to pull the covers and check the wiring at the lights to see if there's a problem there, as well as checking the switch.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.