Those ones had a 40” Surefire tape switch, I don’t believe they sell them anymore. The switch was routed into the stock and the pad was cut into a pocket beneath the rubberized pistol grip. So you’d activate it like a pair of CTC laser grips. The excess wire was stowed in the void or the buttstock.
I milled a groove for the wire along the inside of the grip. Here is the grip with the rubberized overmold removed. The biggest issue was these old pads had a lot of dead spots in them. The newer ones are better, but there are no 40” options.