You can do it, but as said above you would have to by-pass the Rear Door ECU and the Body ECU in the existing circuit, and run two new switch wires all the way to the back door. You can't use the existing wire as that is a multi-purpose 'communication bus'. It will also require a full-time heavy duty 12V+ source wire from the battery to the liftgate and tapping any existing full-time 12V+ circuit in the dash for the switch signal. (The window motor is too much load for the existing full-time supply to the liftgate.)
You then need to wire two standard Bosch relays to the red (up) and green (down) wires to the rear window motor and to the new signal wires and the new power wire (plus tap the existing window ground. This diagram shows what you have to do. Where it says Driver's think Rear, and where it says switched, think battery full-time. The two 12V circuits (switch and motor) would then be separate, not connected as in the diagram here. Likewise the grounds.
Easy Peasy. It would then be easy to piggyback a second switch to install in the back if you want to sleep back there.
Here is the existing circuit.
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'99 4Runner SR5 5spd 3.4L V6 4WD(U.S), original '99 Talls in front, OME 906s in back, Hella fogs, Trekmaster shocks in front, Billy in back, no running boards, FIAMM horns, Alpine sound, Michelin LTX M/S2's, owned since new.
'97 HiLux SW4 5spd 4WD(Japan model bought in Brazil assembled in Argentina, very close to a 3.0 4Runner/Surf)
'71 FordWillys Jeep CJ5 (with straight six Ford Maverick 3.0 liter engine--lives in the mountains north of Sao Paulo Brazil)
My Backyard Frame Swap
