I've been thinking about the specific pogo connector pinout to see if I can find a solution that won't damage components if the wrong tool was installed. With an 8 channel relay, each Slime will have:

1. 24V or Mot1*
2. Toggled GND or Mot1*
3. GND or CAN1
4. Thermistor or CAN2

*Mot2 will be on the other slime.

The first option is the one selected when the relay signal is 0. Pins 1-2 will share a signal pin, as will pins 3-4.

The reasons for the pinout choice:

• Say that the Spindle is expected but the Slight is plugged in. A voltage of +/-36V is applied through Mot1/2. The heater, connected to pins 1 and 2 will see a potential difference of 0V, as will the CANbus tool.
• Then there's the opposite situation, where the Slight is expected but a Spindle is plugged in. 
  • If a thermistor is used on the Spindle, then the mismatch won't be detectable and pins 1 and 2 will be shorted. 
    • The Manta M8P seems to have harder-to-replace fuses than the Octopus Pro, so inline replacable fuses would be used instead. Alternatively, since there's not many mentions of installing a thermistor with a spindle, it can be ommited and a MINTEMP error will occur in this scenario.
    • Expecting a CANbus tool and receiveng a Spindle will result in a short, so a 9A fuse would be needed anyway.
  • Wait a second. What about a diode from Pin2 -> Pin1 inside the Spindle? The Spindle motor will be connected to Pin1 and take current from both pins when operating normally, but 24V to ToggleGND will have a large resistance.
• The next scenario is expecting a Slight but a CANbus tool is connected. The resistance over pins 3 and 4 should be 120 ohms, which seems lower than what a thermistor would have at 300C printing temperatures [reference]. A MAXTEMP error should occur.
• The last scenario is expecting a CANbus tool but a Slight is connected. CAN1 will be grounded and CAN2 would be a 4.7 kΩ pullup to 5V. CAN will tolerate one of the lines being connected to ground [reference].