I'm sorry to hear it still doesn't work.
Let me make a summary of the test you've done: you've only interchanged the connections (cables) and not the motors.
Finally, you ended up having the
left motor connected to the
right connector on the
GoPiGo and vice-versa.
Having this setup, the only motor that kept on working was the
right one, whilst the other one was "dead", even though it wasn't stuck by any means.
If this is what you've described, we can assume you have a faulty motor.
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After you've confirmed, please contact our support by following this website and go to
General Questions and Feedback and briefly explain your situation and someone from our team will contact you for further procedures.
Again, I'm sorry for having this issue. Hope we can solve it ASAP.