Have you taken the side panel of & stuck a meter on the electrics mate before you take the rear panel of, do that 1st as all the wiring comes into the there from the underside plugs.
Dont remove the rear until you've checked the side wiring, continuity tests should yield something as the switches just create a circuit, so stick the meter on the switches & see when you operate the switches for lumbar that you get continuity with the red/black probes either side of the switch, this then proves the switch is ok, then check the wires as if its a break in the wire then the meter continuity test should help determine that.
Taking the seat apart is maybe not the solution mate, could be a broken wire from the seat movement, maybe a cable has got caught when moving up/down/back/forth etc etc.