2 things..
First, look here:
http://www.airsoftcanada.com/showthread.php?t=60410
I have pics on how to run the wiring. Read the whole thread. There's good info in there.
Second, the washer that's used to hold on a crane stock is not fully rounded. There's an edge cut off so that the wires can run freely in the stock. With the standard washer, you'll pinch your wires and cause a short circuit. You can mod the standard washer by dremeling off a part to allow the wires to run freely.