As the pickup is new all your electrician buddy (EB) need to do is solder the ends of the grey lead to the correct places on the wiring harness; the hot wire to the lug on the selector switch and the braided shield to the case of the neck pickup volume pot. The black wire with the round lug on it should be slipped on to the treble side height adjustment screw for the pickup, between the top of the spring and the underside of the pickup surround.
Here is a schematic of the wiring from RIC that can guide EB.
And here is a photo of my former July '73 4001's wiring harness so that EB can see where the wires go:
4001 Control-Wiring_800_02.jpg
The grey lead that has the 90º curve to the left coming up from the bottom of the photo is the one coming from the bridge pickup.