There are a few items that are only fused thru the 200 amp fuse in the little box next to the battery, an example is the ICM (Illumination Control Module - headlight switch).
At the point you were at, the next step is to pull all the fuses from the ICM.
If that does not do it, pull the big red cable off the back of the alternator.
If that does not do it, pull the little wire/connector off the back of the alternator.

WARNING: Unbolting the alternator, if you keep it away from ground (the engine block), is the same as pulling BOTH wires off the alternator - so if you unbolt and dismount the alternator and the current goes to zero, pull the heavy red cable and tie it back, then remount the alternator to see what you have. IF you have current again, pull the little wire/connector and then re-mount the alternator for a second measurement.