What is the BROWN Alternator Wire for?

[rodstored-72]

I like this.. a lot of good information here. it is falling in line with a question I have. I have a '86 c10swb that had a 305 and Silverado package. If I understand right the same brown wire on my harness would be the volt meter supply (?) wire? also I am curious how it plays in relation to the current LS swap, which I am in the middle of? it is connected to a 2 prong connector that has a H.D. red wire that I believe ran directly to the batt. or junction block that was attached to the firewall above the engine.
thanks!!