And again: What does this part ??!

[Rob73-87]

Hi everybody,

I´m still sorting out some electronical stuff, wires and so on, that I don`t need any more.
I managed to get rid of the cruise control stuff - now I need to know what wires were esspecially designed for the diesel engine under my dash (fuse box...) - you remember: I swapped my engine because the diesel wasn`t complete.
The other problem is, I ordered an ac delete cover and now I`m confused about all the wires that went originally to the ac system in the engine compartment...which wires do I need for my fan and which wires can be cut out ???

Here are some pics...very big as usual...sorry for that...

at first: I discovered that plug in the firewall, - bottom left - does anybody know for what it is ?



the next pic shows all the wires and plugs from my old ac (as I got the truck the ac was already missing...)
can you explain which ones I need for my simple heater fan in my ac delete cover ?



Another pic a little closer...




thank you for your help guys -