Wiring harness rats nest

I inherited this mess and I'm very unsure where I should be getting power for my fuse block. I know where every wire goes in the last Pic except for the large red one. It seems like it may have been connected to the alternator at one point in time. I also see a bunch of cut wire coming from the firewall. It does have a DUI distributor so I'm guessing some of these were for the ignition module. I've searched through wiring diagrams and it seems there should be a yellow wire that puts 12V into the cab. I don't see a yellow wire anywhere here.