Hmmm... I'm not finding a good wiring diagram for the heaters in a Runner. BUT-- am willing to bet the blower resistor is bad. Seems to me the rear heaters have their own elements. At least my '99 is set up that way.

The resistor is either behind your blower motor, or next to the AC unit near the AC and heater fuse block behind your glove box.

Go here

In the '96 FSM, go to the end of the FSM, then back up to page AC 36 or AC38, and you'll see the checkout for the blower resistor. At least that'll give you an idea of what you're looking for.

You can find them in a junkyard, or from the dealer for under $25.

If you still want a good schematic, for $10 for 24 hours you can download away at www.techinfo.toyota.com. The '93 FSM we have sticky'd over in the early trucks section doesn't have the resistor shown that I can find.

Hope that helps!