Quoted from wayout440:
If I am understanding, you are trying to use the games control signal/driver to turn on the mod? If so, you should use a relay to turn on the mod. You will tie the ground from the mod supply to the game ground, but this is a safety ground only. you can't tie a negative voltage from your mod power supply back into your game supply.
Ok, my apologies, I don't think I'm explaining this right.
The mod in question is a motor that turns when the software in the game tells it to. Unlike typical mods, this one was a feature of the game that was originally cut from production because of costs, and they re-added it later. The actual game software tells the motor to spin at certain times, using one of the previously unused pins on the power driver board
For this to work, the mod typically gets it's power from the game's internal 5v power, and the negative (black) wire is tied back to the game's power driver board on a specific pin that completes the circuit when the game software tells the motor to run.
Since I'm moving this to an external power supply, my 5v (red) positive lead is coming from the new power supply. I still need the mod's negative lead to tie back to the game power driver board because the game still tells the mod when to spin. Therefore, the mod's black wire is run to J125 pin 3 on this WPC 89 power driver board (ToM).
However, that leaves me without running the negative (Black) lead from the power supply to anywhere. I assumed I should run it to ground, because if I don't run it, the circuit isn't complete and the mod won't spin, at least I think so.
I ran it to ground and it works, I'm just wondering if this is the right way to do it?