2. Check the dimmer switch. The dimmer switch for the interior cab lights is located on the instrument panel. If the dimmer switch is set to the highest setting, the lights will stay on even when the doors are closed. To check the dimmer switch, turn it to the lowest setting and see if the lights turn off. If the lights do not turn off, you may need to replace the dimmer switch.
3. Check the wiring. If the door switches and dimmer switch are working properly, the problem may be with the wiring. To check the wiring, you will need to use a multimeter to test the voltage at the light switch. If there is no voltage at the light switch, the problem may be with the fuse or relay.
4. Check the fuse. The fuse for the interior cab lights is located in the fuse box under the hood. If the fuse is blown, the lights will not turn off. To check the fuse, open the fuse box and look for the fuse labeled "Interior Lights." If the fuse is blown, replace it with a new fuse of the same amperage.
5. Check the relay. The relay for the interior cab lights is located in the fuse box under the hood. If the relay is faulty, the lights will not turn off. To check the relay, remove the relay from the fuse box and inspect it for damage. If the relay is damaged, replace it with a new relay.
