I have a Quicksilver Commander 3000 series remote control on my boat-how do I take it apart to check cables inside?

Find yours listed, see if this helps.

Mercury Parts, ACCESSORIES REMOTE CONTROLSVOLUME 2 (http://www.crowleymarine.com/mercury-outboard/2436.cfm)

There is a Button that allows you to move the control handle forward to increase engine idle while disengaging the transmission lever to place outboard motor in gear. This Button allows you to idle the engine at higher speeds while engine remains in neutral. The Button is centered in the fulcrum of the handle.That plastic Button comes out when you pry on it with a straight blade screw driver. Pry it toward you. Behind this button is a brass hex nut with a hole in the middle of it. Remove that brass nut and that is all there is to it.
The process is very cryptic, but simple when you figure it out. If you are not told about it, chances are you will not find this simple solution.