I wonder if someone fitted 100w bulbs back in the day (before Osram/Philps started making brighter but correct wattage bulbs), i did just that on my Sierra many years ago, didn't melt the connectors but melted the column dipswitch instead, ended up fitting relays near the headlights.
Or possibly did someone bodge wire a pair of spotlights in at some point taking a feed from the main beam cables at the bulb?