Following up- so far all of the wires driver-side look fine. Everything seems to be connected and runs through the giant red wiring harness from the dash to back of bus.
Looking at light bulbs and sockets now -reading prior posts I see sometimes there can be corrosion causing a bad connection.
I might have one bad bulb, it looks a little blackened, and its pair is an amber bulb - so I'm going to get a new pair now.
Attached pics of the fuse box (sans brake fuses) and dash-side wiring harness for reference. Im kn mobile now so apologies if they attach weird.
The red and orange cut wires in the harness were for the side and rear emergency door alarms, they ran to little pressure switches in the door frames. I tested brakes after disconnecting these and everything worked so I don't think that is the problem. They were the only wires removed from rear of bus aside from the speaker wires (so, so much speaker wire!)
There is one fried connection in the "rats nest" (what do you call this anyway?). The connection runs from the bus bar to the Master Sw connection on the yellow 'Eight Lamp Bus Flasher" terminal.
Last but not least, there are a bunch of relays under the hood, in front of the driver on the firewall. Any idea what these do (before I trace them all over the bus)?