The 1990 Toyota pickup truck was equipped with a single heater control switch. Unlike most earlier heater switches, the switch on the 1990 version was electrically powered as opposed to cable-operated or vacuum-assisted. The advantage of an electrical switch is its reliability, but a defective switch must be replaced. Fortunately, accessing and replacing the switch generally takes only a few minutes and requires only minor disassembly.
Remove the screws that secure the trim panel around the heater switch with a screwdriver, then remove the trim panel.
Pull the knobs off of the heater's control panel.
Pry the bottom of the heater's control panel upward with a small pry bar to remove it.
Pry the bottom of the front of the heater switch off of the control panel with a small pry bar.
Trace the wiring loom from the back of the switch to the wiring connection, then pull the wiring connection out of the truck's main wiring loom.
Pull the switch out of the control panel.
Feed the wiring loom attached to the new switch through the front of the control panel and press the switch into the control panel until the switch is secure.
Plug the wiring connection into the truck's main wiring loom.
Press the heater's control panel into position until it snaps into place.
Press the knobs onto the face of the control switch.
Position the trim panel over the heater switch, then install and tighten the panel's screws with a screwdriver.
