* Blower Motor Resistor: This controls the fan speeds. A failure here can mimic a relay problem.
* Fuse: A blown fuse will prevent the heater from working. Check the owner's manual for the relevant fuse.
* Relay (likely within a larger system): The relay itself is often part of a larger under-hood fuse box or a central control module. It might be a component within a body control module (BCM) or a part of a larger relay assembly.
To find out if there's a relay involved, and which one, you'll need to:
1. Consult your owner's manual: Look for wiring diagrams in the repair section. This is the best way to trace the circuit.
2. Check the fuse(s): Replace any blown fuses before looking further.
3. Examine the under-hood fuse box and relay panel: Look for a relay that corresponds to the heater blower motor. The wiring diagrams will help. Many relays are similar in appearance, so relying solely on visual inspection is unreliable.
4. Check the blower motor resistor: This is often located under the dash, near the blower motor. A faulty resistor can cause intermittent or no operation.
5. Use a wiring diagram: A wiring diagram specific to your truck's year and model is essential for proper diagnosis. You can often find these online through forums dedicated to your truck or by paying for access to a repair manual.
In short, a relay is almost certainly involved, but its identification requires more than just looking for a label. You need to trace the circuit using the wiring diagram.
