1994 Chevy 1500 starter wiring -please help! its all different!!

Hey folks need some help finding out about how
the original wiring goes for this 94 K 1500 pickup.
I'm trying to get it fixed up for my mother, as my
step father recently passed away and he was the
wrench around the house. It was his truck and he
had done some alterations and modifications
throughout the years..for whatever reason, he was
replacing wiring with colors that didn't match the
original so I'm pretty much starting from scratch
between alternator the ignition switch Etc. I've got
the purple larger gauge wire going from the S
terminal on the solenoid two my ignition switch,
but that's about it. Small black and brown wires
coming out of firewall on driver side go where? I've
included some photos of my issues. any help
would be much appreciated! thanks