Your hot connections are not road worthy, but they should give some life to the starter. If that is the battery ground I see in your small pic (grounded to the bell hsg) and it's really that dirty/rusty/painted not shinny metal as Bill indicates, that's your problem. The flat spot, the bolt, the washers, the cable end, all have to be bare! metal. NO GREASE! NO PAINT! NO OLD RUST OR OIL. That's on every grounding spot. You need to ground battery to bell hsg/eng, eng to body, body to frame or your switches and motors and lights will not work. Assume you checked 12V battery feed by touching the exposed copper strands down at the starter to see 12V, then touch the solenoid contact also. What are you touching your ground test lead to? Shinny spot on starter or motor or what, when you get .5V. Should use store bought, factory terminated, shrink sleeved, new, battery cables. Not DIY.
