The thin blue wire, connects to the alternator, depending whether you have a pre 86 alternator or post 86 (should be post 86 but you know theres some wierd and wondeful people out there that like to do some crazy shit )

So, yours being the correct alternator, should have its own push fit round plug on the blue wire onto the alternator, and they all also have an inline round plug aswell joining to the main loom.

I would remove them, give them a quick once over with a bit of scotch pad or something, then apply a bit of electrical contact grease and put them back on