Welcome aboard RafaelDP89!!!
You had somewhat hijacked an older, semi-related thread. I've moved this post to its own thread.
In DC (12v/24v) Black is the old standard for the ground (common ground). The new standard is moving toward yellow for the common ground in DC. This is in an attempt to differentiate DC from AC, which is also using the Red/Black color scheme.
To me, it would look like you have 3 grounds there. Even if they chose to use yellow as the positive, you would still have two grounds. I would assume that, since the grounds are common, they are simply tying multiple grounds together at that junction to act like a 'bus'.
In other words, think of a single run of ground wire that needs to be tapped into, like a "T". You'd have to cut the ground wire, then tie the ground from your device into that leg of the circuit. Voila, the process of cutting the ground now leaves you with two black wires in your hand. Maybe they ran another (yellow) ground over to that junction??
Where is the positive in this mess? I would get a multi-meter and start taking readings.