Starter won't crank when rear brake held, will start with front brake

[WildIsland]

Hey all - this is my first post, I have a 50cc icebear trike, and so far it's been great. One issue has come up that I haven't been able to figure is this:

When I hold the rear brake, the starter won't crank/no noise at all. However, when I hold the front brake, it cranks and starts up fine. Also, when I press the rear brake, the brake light does turn on. So, I've played around with what I think all the wires, and I'm just at a loss at what the issue could be.

Would anyone know what this type of issue could be? Wire diagrams get super confusing, but I've double checked all the connections I can see at least.

Thanks in advance!