1-29-051023 EST  Look in front of the passenger footwell. Like above
where your feet would be if you were sitting there.  It will be a
squareish thing with 3 or 4 wires connected in the plenum.  Handle it
carefully if you take it out. It reminds me of a toaster wire.  If you
go to the dealer to get a replacement, be sure you give them your vin
so they can get the proper one.  Good luck. Ed

My Toyota original 1985 4runner manual doesn't show the location, but it
shows a blower relay located behind the glove-box area under the dash-board.
Logically speaking, it has to be between the blower switch and the blower
motor.
I know the resistor for the rear blower is in the console with the switch,
which has two speed positions.
Some north american vehicles placed the resistor in the air-flow of the
blower to cool it, others placed it on the firewall in the engine
compartment. My guess is that it is under the dash-board. It has a connector
according to the manual, so it is not hard wired.
I replaced the brushes in the blower motor about 3 years ago, my vehicle is
a 22RE with 374,598 km on it. You may just have worn brushes. The brushes
are easily replaceable, the motor was made to have them replaced, but Toyota
does not sell replacement brushes. I took the brushes to a motor shop,
bought some similiar types that were slightly larger and cut them down on
the sides with sand-paper to fit the holders. Two brushes, with an embedded
multi-strand current wire coming from the side, not the end. The holder has
a slot for the current wire to slide down as the brushes wear.  An '89 would
likely have worn brushes since the blower-motor runs all the time the engine
is on, unless you deliberately turn it off with the switch. The motor is
easy to remove, connector plug and a couple screws, then take it apart for
access to the brushes. Mark the motor bearing end-caps and the motor body to
ensure it goes back together the way it was... and soak the bearings in oil
while its apart.