I mainly just want to know what the melted blue wire is but also curious on what the 3 prong connector is
it’s a 1985 w-150 360
new to forums so lmk if I’m doing anything wrong

What, if anything, doesn't work on the truck?

Evidently a previous owner bypassed rather than repair a burned fusible link. These are protections built in to keep the truck from burning to the ground. I suspect the three prong connector might be for an option that wasn't installed. Most vehicles have those somewhere. Like HeyYou said, what isn't working?

Silly question, but is this a left or right hand drive vehicle? Some of the photos are of an odd perspective. It looks like the booster for the brakes is on the right hand side.

the 3 prong plug is for a egr timer or something emissions related which is likely long gone. does the charging system on the truck work? the large wire is generally for the alternator. the 2 orange fusible links power most of the stuff in the cab.