Here's a systematic approach:
1. Check the obvious: First, verify the main fuses and relays under the hood. Look for blown fuses related to the rear power circuits (your owner's manual should identify these circuits and their corresponding fuses). Replace any blown fuses. If the fuses keep blowing, there's a short circuit somewhere in the rear wiring harness.
2. Locate the rear fuse panel: It's typically located in the cargo area, often under the side panel or behind a cover. Access it and visually inspect the fuses within. Replace any blown fuses.
3. Test for power at the rear fuse panel: Use a multimeter to check for 12V power at the main power feed wire(s) going into the rear fuse panel. This is crucial. If there's no power at the input, the problem lies *before* the rear fuse panel.
4. Trace the power wire: If no power at the rear fuse panel input:
* Follow the main power wire: This usually runs from the under-hood fuse box to the rear. You might need to consult a wiring diagram (available online or through a repair manual). Carefully trace the wire for any breaks, corrosion, or loose connections.
* Check for relays: There might be a relay involved in supplying power to the rear fuse panel. Check its operation (some relays click when energized; you can check continuity with a multimeter).
* Inspect connectors: All connectors along the wire's path should be checked for corrosion and secure connections.
5. Check the Ground: A poor ground can also prevent power from reaching the rear fuse panel. Locate the ground wire for the rear fuse panel and check for corrosion or loose connections. Clean any corrosion and ensure a secure connection.
6. Short Circuit: If fuses keep blowing after checking connections and grounds, you have a short circuit somewhere in the wiring harness. This requires careful and systematic tracing of the wiring to locate the short – a difficult task that often involves removing interior panels to access the wiring.
Important Considerations:
* Wiring Diagram: A wiring diagram specific to your 2003 Trailblazer is essential. This will show you the exact path of the power wire and any associated relays.
* Safety: Disconnect the negative battery terminal before working with any electrical components.
* Professional Help: If you're uncomfortable working with car electrical systems, it's best to take your Trailblazer to a qualified mechanic. Diagnosing short circuits can be very challenging.
This detailed approach should help you locate and fix the power issue. Remember to test for power at each stage to narrow down the problem area.
