What if the module does not work even though all connections seem correct? The LED stays dark. Or bad contact

A common and often recurring problem. If multi meters or other equipment is used to verify the power and ground connections to the module, the little square contacts in the Molex plug might have been damaged.

This is what the contacts SHOULD look like. Leftmost ones are power and ground.

Damaged contacts as a result of using multi meter tips and jamming them too hard into the plug:

This is how to fix the problem. Use a needle and stick it between the contact and the plastic to the left and to the right of the contact.