The rear washer is protected by a 10Amp fuse marked ECU B, it sends power to the body control computer and gets grounded through the main rear wiper switch. The back door control module (rear tail glass and wiper motor) has a 30Amp fuse marked Power in I think the fuse box at the driver's left foot well area under the dash.
Check for broken or damaged wires where the wires go out to the tailgate from the body of the truck.
The 4Runner has a "feature" where the rear wiper and the rear defroster will NOT work if the rear window is down - even the slightest bit. So roll your rear window up all the way, and I bet your wiper will work. I learned this by taking my 4Runner to dealer while under warranty, and was a bit embarrassed when they told me the "problem."