Right, he took a taillight from another Fusion, put it in my car and it didn't work. But the strip of LED light I'm referring to, the outer red strip, lights up when the doors are open or shut, so wouldnt that mean the circuit is complete? However, the same red strip (see image) is supposed to light up while I'm driving.
Hi smbarr. Yes, I understand exactly what is happening. The point I am trying to make is this: If a working taillight from another Fusion was connected in your Fusion and did not work,
then the issue is not with the taillight unit itself, it is with a circuit/module/system/BCM etc. in your Fusion, not a problem in your taillight unit.
So you can eliminate the taillight housing itself as a possible problem area.
You asked...
"So wouldnt that mean the circuit is complete?" The answer is no, because the circuit is not complete at all the times it should be complete, since it does not light when you are driving. There is an issue in the BCM, a module, relay or some other electrical/electronic area of the system/circuit.
And it is not a problem in your taillight housing, since a taillight housing from another Fusion (which works perfectly fine on the other Fusion) does not work properly on your Fusion. So...it is a problem somewhere in the electrical/electronic "circuit" of your Fusion.
There is no way to accurately diagnose the precise issue blindly over the Internet. However, the scenario you have described points towards it being an issue somewhere in the electrical/electronic system of your Fusion, not the taillight housing itself.
Perhaps one of our tech members will be able to jump in with more help. Keep us updated and good luck.