What is the BROWN Alternator Wire for?

[Gregski]

first of all guys nothing is broken I am not trying to fix anything, this is just to help me and anybody else who comes across this thread to understand what the brown alternator wire is for

second, I would like to keep this discussion on point and I will start a new different thread to go over other wires for the alternator so that it is easier for folks to search for and find specific information that they need (finding stuff can be frustrating sometimes) even though its been covered here and discussed already

also posting this specifically in the 73-87 area since I don't know if the functionality is the same for the prior generations ie 67-72 for example

so on a 1974 1/2 ton truck 350 V8 4 spd manual 2 wheel drive no AC, I have removed the wire harness conduit and traced the BROWN alternator wire all the way from the alternator to the plastic black square bulk head connector on the firewall

and I have to ask what is the brown alternator wire for?