Here's a general guide, but always consult your vehicle's repair manual for precise instructions and diagrams specific to your model:
1. Preparation:
* Disconnect the battery: This is crucial to prevent electrical shocks and short circuits. Disconnect the negative (-) terminal first.
* Gather tools: You'll likely need a screwdriver (Phillips and/or flathead), possibly a panel removal tool (to avoid scratching the interior), and possibly a wiring harness adapter depending on your new speakers.
* Purchase replacement speakers: Measure your existing speakers before buying replacements to ensure proper fit. Note the impedance (ohms) and wattage to select compatible speakers. Most aftermarket speakers will fit, but you might need adapters.
2. Accessing the Speakers:
This is the most variable step. The rear speakers in a 1999 Sierra Extended Cab are typically located in the rear side panels, possibly behind panels in the rear side of the cab. The exact procedure varies:
* Locate access panels: Carefully examine the rear side panels of your truck. Look for screws, clips, or other fasteners holding the panels in place.
* Remove panels: Gently pry the panels away from the door or side using a panel removal tool or a flathead screwdriver (wrapped in tape to prevent scratches). Work slowly and carefully to avoid breaking any clips. There might be several clips holding the panels in place.
* Locate the speakers: Once the panels are removed, the speakers should be visible. They're usually mounted in some sort of frame or bracket.
3. Removing the Old Speakers:
* Disconnect wiring: Unplug the wiring harness connector from the back of the old speaker. Take a picture of the wiring connections before disconnecting to help you remember how to reconnect them.
* Remove mounting screws: Unscrew the screws or bolts holding the speaker in place.
* Remove the speaker: Carefully remove the speaker from its mounting location.
4. Installing the New Speakers:
* Mount new speakers: Carefully align the new speakers in the mounting location and secure them with the original screws or bolts.
* Connect wiring: Connect the wiring harness from the new speaker to the existing wiring harness. Make sure the positive (+) and negative (-) wires are correctly matched. If your new speakers' wiring doesn't match your truck's, use an adapter or wire the connections correctly.
* Reinstall panels: Carefully put the panels back in place, ensuring all clips are properly engaged.
5. Testing:
* Reconnect the battery: Reconnect the positive (+) terminal of the battery.
* Test the speakers: Turn on your stereo and test the new speakers at various volume levels to ensure they are working correctly.
Important Considerations:
* Wiring adapters: You might need a wiring harness adapter to match the wiring of your new speakers to the factory wiring. These are readily available at most auto parts stores.
* Speaker size: Measure the diameter and depth of your existing speakers to ensure you buy replacements that fit. Common sizes are 5.25" or 6.5", but yours might be different.
* Wiring diagrams: If you're unsure about the wiring, consult a wiring diagram specific to your 1999 GMC Sierra.
* Professional installation: If you're not comfortable performing this task yourself, consider taking your truck to a professional car audio installer.
This is a general guide; the specific steps might vary slightly depending on your truck's configuration. Refer to a repair manual for your specific year and model for detailed instructions and diagrams. Failing to follow the correct procedure can lead to damage to your vehicle's interior or electrical system.
