The alternator on mine has three wires.
One big one to the B terminal is obviously the main charge supply. Then there are two smaller terminals (which take a special plug but standard 1/4" spades fit them fine): one is 'L' which is the connection to the charge warning light, and the other is 'S' which is the sense wire. This should be run to the battery positive post, though you can get away with just linking it onto the big B terminal - the only problem is that the alternator then won't compensate for any voltage losses in the main charge link.
Every photo of these engines I have seen has had a different alternator unit on so the above may not be the case for yours, but the majority of these Japanese type alternators seem to be of this style.
In answer to your actual query I am not sure where one would attach the rev counter wire to, there doesn't seem to be a 'W' terminal on my alternator - or not a marked one anyway.