those wiring colours and the recommended connections - all sound wrong to me.
Most aftermarket tachos need 3 connections - a 12v+ feed, an earth, and a connection to the low-tension side of one of the ignition coils.
The 12v feed is easy enough to source - normally I just tap into a connection that has a +12v supply when the ignition is switched on. The rear brake light is a good place to source a constant +12v supply without the problem of draining a battery.
Earth - just find a good earth. The mounting bolts for the ignition coils are good.
The low-tension side of the coil - if your coils are marked with a + on one terminal and a - on the other, then connect to the - side. If you can't find any markings - have a look at the colour coding of the wires feeding the ignition coil. Normally, the high-tension side of the coils has a yellow or red wire feeding it, and the low-tension side has a black or green wire. If you are stil not sure - trace back the wiring from the igniter box - you are looking for the wires that come from this box up to the ignition coils.
The colour coding from your tacho - black/yellow trace is normally an earth on kawasaki models. Black should be the +12v supply to the tacho, and green should be the feed in from the low-tension side of the coil. You may have to swap these around to get the tacho working.
Do you have a model number for the tacho, or can post up the wiring diagram ? Hopefully you are not using one of those tachos from Supercheap with the 4/6/8 cyl switch on the back. These are dodgy as and in my experience almost never work on a m/cycle......
