What is this cable for?
 

https://cimg9.ibsrv.net/gimg/5series...869ca46dcb.jpg

Your BST. It seems someone just cut the plug off. Do you have an airbag light on. Is there a resistor soldered on the wires.

That's in the rear, right? I can't find anything identical on mine. I saw an antenna cable going through there and a wire that connected to the powertrain bus but that was all. I know E46s had a hidden wire on that side in the trunk that they put battery tenders on while they were shipping overseas. What color are the wires inside the black sheath? My PT CAN bus wires are red and blue.

seanjordan20 I just got it back from the shop they changed the battery and after that the airbag light was on but i cleared the codes and it hasn't come back yet, There is no resistor on the wires.

It clearly looks like the BST delete but if so, there should be a 2 ohm resistor in place or else the passenger restraint notification will not clear.

Im clueless to what it is then if you were able to clear the code and there's no resistor on it. Unless there is a simulator under the seat deleting it.

Is there a wire coming out of the positive cable connected to another cable. 2 wire cable

I checked and there is a little box thats says mat emulator plugged in under the passenger seat, but just incase should i put a resistor on the loose cable?

No, the emulator is bypassing the issue

Mystery solved.