Some models are equipped with an air bag or Supplemental Inflatable Restraint (SIR) system, which must be disarmed before working near its components. Begin by disconnecting the negative cable at the battery. For models with headlight and wiper/washer switches located in the instrument cluster bezel, remove the bezel and unplug the electrical connectors. After removing the screws, separate the switches from the cluster and use an ohmmeter to check continuity between the terminals; if continuity is not as expected, replace the switch. To access the dash light rheostat, pull off the knob, remove the retaining nut and trim plate, then push the rheostat back through the opening to remove it. Check the operation of the rheostat with a test lamp, which should brighten when the knob is turned clockwise and dim when turned counterclockwise; if it does not function correctly, replace it. For the rear defogger switch, reach behind the dashboard to unplug the electrical connector, squeeze the clips on the sides, and push the switch out. Use an ohmmeter to check continuity between the terminals. For the rear wiper/washer switch, similarly reach behind the dashboard, unplug the connector, squeeze the clips, and remove the switch by pushing it out; check continuity with an ohmmeter and replace if necessary.