I am changing out my speedometer I purchased one from Suzuki Lighting Conversions for $75.00 one with a tach. I heard that they will plug right in and the tach wiring is already ran all you have to do is plug it in. I noticed that there are 4 wires a red, white, and blue that plug in to other wires that were hooked up from the original tach, there is a black wire at the top center of gauge cluster  i don't know where it goes any suggestions would be greatly appreciated.

The red, white, and blue wires go to a check engine light reset switch, that is located on the brace bar on the lower part of the dash.  You do not have to hook those wires up to the switch, if you do not want to.  If you don't hook them up, what it does is keep the CEL from coming on, when the odometer reaches a specific mileage interval.  The CEL will still come on, if there is a "real" fault detected.  Then, in that case, if you fix the fault, the CEL will go off.
The black wire is associated with AC.  So I would pull the rubber cap off the back of the cluster, take the nut off, and remove the wire and put the nut and cap back on.

And you are correct, in that if the tach cluster is one from an 86-88 samurai, and you have an 86-88 samurai, that the tach cluster will fit and plug right in.

thank you I also noticed a switch under the dash when near the red, white, and blue wires does anyone know what the switch is or does

actually now that i read again it must be the check engine light switch haha thank you

actually now that i read again it must be the check engine light switch haha thank you

Correct.  That is the CEL reset switch.