The rear brakes on both of my Bonneville'* appear to not be working. The rotors have developed rust on them. Calipers and pads are not that old. Is there a reason these are not auto adjusting? The parking brakes are not hooked up on either one.

Two cars' worth of this at the same time?

Does the brake pedal go down a lot before any brakes engage?

Is the brake reservoir empty?

Is the [brake] light on?

Is rust building up on the swept surface of the rotor or just the edge?

Brake pedal does not go down. Reservoir not empty. Brake light is not on. Rust is on swept surface of the rotor where the brake pads should be keeping it shiny clean like the front.

Both have non functioning parking brakes with the cables not hooked up to rear calipers. My suspicion is that this could have something to do with it.

Just process of elimination here: Two Bonnevilles with the same rare problem with the same related parts disconnected, seems like you should probably reconnect the parking brake systems on these.