I just installed a G&P crane stock, from illusion
on my m4 awhile back. There is a good guide here on ASC that tells you how to wire it correctly. A few things i may note is, that if you got the G&P one, with an 8.4v battery, youll need to cut maybe an inch or so off the buffer tube, otherwise the battery wires get pushed down by the tube when you retract the stock. The wires will get cut up and broken if done repeatedly...i learned the hard way!
Since you have an m4, your gonna need to rewire the mechbox to the back... i HIGHLY suggest doing it like this, i didnt run one solid piece of wire, and i really regret it now, big mess inside my body, but it works so im still happy, someday soon im gonna rip it apart and rewire and clean it all up.
http://www.airsoftcanada.com/showthr...e+stock+wiring