This 1993 BMW 318IS came in with the complaint that the battery would go dead after a few days of driving. The battery and the alternator had been changed, with no success. The first thing I spotted when I opened the hood and look at the alternator was a 12 gauge red ground wire, that has been quite hot. European manfacturers generally use brown wire for primary ground circuits. I suspect a local American, with very little electrical knowledge, has been in here.
The wire color does not really matter that much but the size of the wire and the type of termination does.
The other end was connected to a small bolt on the side of the intake.
Now, for a little BMW charging system 101. BMW historically mounts their alternators using rubber bushings to prevent vibrations (keeps them quiet and smooth). This requires the alternators to have a ground wire between the alternator and chassis ground. The alternator on this vehicle is somewhere between 90 and 120 amps. The ground wire has to be adequate in size to carry the full output of the alternator. This red wire shown below, would have never handled that much current and obviously did not.
To get a better look at the alternator, I put the vehicle in the air and looked at the alternator from the underside. If you look at the center of the picture below, you should see the empty hole were the ground wire should have been attached.
I made up an 8 gauge ground wire with heavy ring terminals and heat shrink tubing. Then, I attached one end, to the alternator ground.
The other end attached to the aluminum bracket, shown below. I was concerned about the wire being damaged by the steering shaft at some point, so I did a couple of things to prevent that from happening. First of all the wire is heavy enough that it would be unlikely to fall onto the steering shaft. Next, there is a plastic bracket that you cannot see in the picture that I routed the wire into for support. I controlled the length of the wire also, to eliminate any excess.
The charging system is back working as designed. It turns out that engine in this vehicle has recently been changed and there a quite a few issues that were left unattended. I recommended that the customer take it back to the installer to finish the job.