OK, since I've gotten Cooper, the OBC has informed me that I've been dealing w/ +122F ambient temps all the time!! My sensor was mounted behind the lower mesh grill, where I anticipated finding it, but the was no wiring plugged into it. I found the sensor plug behind the left turn signal light, but the clip was broken and the temp still read +122 even when plugging the sensor in.

So I ordered a sensor and pigtail from ALLMAG, but upon wiring that in, I still show +122. Closer inspection of the wiring behind the turn signals indicates that someone has done a hack job to poor Cooper's wiring. It appears as though someone has spliced in wiring for aftermarket horns, and everything is wrapped in electrical tape instead of split loom or shrink tube. I actually found that I haven't had a right hand parking light all along. The wires were broken off right at the fixture. I managed to get the terminals out and repair that, at least.

Anyway, further research indicates that +122F means that I have a short to ground somewhere, correct? The E36 Youtube video I found says that the ambient temp sensor is a metered ground connection, should I then see some level of closed to ground always (I wouldn't think so)? Both wires at the splice read ~2 ohms measured to the grounding lug right beside the left hand headlight area.

It looks like that bundle of wires runs underneath the engine bay fuse box and then makes its way through the firewall, is that accurate? Is there someplace that I should focus my initial search for this short?

I can say that my wire colors don't match the ones on the pigtail I received, but I've seen that before when replacing factory stereo harnesses from donor vehicles, so that doesn't really concern me. I just find it strange that everything else in that bundle of wires works fine (turn bulb, parking light, horn, foglight, etc), but that the temp sensor seems to have managed to short to ground.

Also, just for my information, what is the flat black assembly bolted in right next to the turn signal area that sends quite a few of its own wires into the same bundle?
It looked like #4 in this image:

 

So the wiring I'm dealing with is #1 in this pic from realoem. It this showing that it stops at a connector in the engine bay, or does it terminate in the dash somewhere?