here is a picture of it didnt have a chance to take one. found that Merzbow had the same problem with his tahoe build
OK, with my GM service manuals in hand I've been reading up on the charging system in this vehicle in preparation for the immense amount of work I have to do here. Guess what this is:
That's the "battery current sensor" clamp. It fits around the negative cable from the battery to the frame. (Actually, there are TWO negative cables, a big one to frame and a small one apparently just for the headlight assembly return path, but whatever.) This sensor feeds into the BCM (body control module), which also measures voltage. Using these data, the BCM controls the alternator (by adjusting the field current supply, I think).
So what's the big deal? Every high-output aftermarket alternator company recommends replacing ground cables from the alt and battery to the frame with 1/0. Great idea, except that if your car has some bullshit like this current sensor hanging off the battery negative cable, and you DON'T migrate that to the new cable, your charging will be FUBAR. Just keeping the OEM cable connected and running a new 1/0 cable is NOT sufficient because the clamp will NOT see the current running through the new cabling. [EDIT: fixed paragraph for accuracy]
So what to do? Luckily, it appears this clamp will fit around a 1/0 cable. (The OEM cable is apparently 4-gauge.) So I think I can just do a straight-replace on that cable.
Note that there is no way this clamp would fit around MULTIPLE negative cables, nor is there any way to have the BCM control more than one alternator. This is why, if you do a multi-alt setup in this vehicle, it appears best to completely isolate the extra alternators and their batteries (which is what I'm doing).