[gone-ot]

...BEFORE you cut into anything, did you consult the factory schematic to see what the "color-code" is for the wire(s) you're after?

...and, here's a "tip"--instead of cutting thru any insulation, simply solder the signal-wire to a hefty straight pin and simply stick the pin thru the insulation and tightly wrap the area with electrical tape (about ½-inch on either side).

*** DO NOT stick the pin thru the wire from top to bottom; rather, slide the pin under the insulation like the nurses do the needles when you give blood.