Gear Tooth Sensor FIRE

[Aaron_H]

Greetings,

This past friday, our robot caught on fire in a catastrophic failure of the gear tooth sensor. The way we hooked it up is as follows (I know its wrong):

PWM cable from the J1 (12 v and G) solder connections on the sensor to digital input 1..
No connection to the breaker panel.

This configuration caused the wire to heat up so that it combusted. Today, with the remaining gear tooth sensor, after realizing it was originally connected in the wrong fashion, we connected J1 Black to Ground and White to the Positive side of the breaker. We connected J2 Black, Red, and White, respectively, to digital input 3. This caused one of the speed controllers for our drive motors to trip the breaker panel. Somewhere in the process, the pwm cable going to the robot controller heated up again and melted, but did not ignite since we caught the problem earlier. Does anyone have any clue as to what might be wrong? Also, the wire that melts is always the ground wire...
Thanks in advance