I don't know what kind of chip you have but on my Xecuter2.0 Lite, there are 3 jumpers on the top and one of them is the on/off jumper. What i did was went to Radio Shack and got a toggle switch and some wire and soldered a wire from each of the posts the jumper connects. Then i soldered those wires to the positive and negative terminals on the switch and put the switch on the back of my xbox to the right of the ethernet port when looking directly at the back. i can now turn on or off my modchip with a switch.
that i don't know but you might want to check out xbox-scene.com. your chip should be there or it may have come with a piece of paper telling which jumper does what. if not, see if the chip itself says "on/off".
Also remember to get any use out of an xbox with a modchip fitted, and disabled, you have to have a locked hdd, and the MS dash.