* Battery and Cables: This is the *first* thing to check. A dead or weak battery is the most obvious cause. Also inspect the battery cables (positive and negative) for corrosion, loose connections, or damage. Clean the terminals thoroughly with a wire brush and baking soda solution if needed. Make sure the cables are securely clamped onto the battery posts and the battery itself is securely fastened in its tray.
* Battery Cable Connections: Even if the cables look okay, a poor connection at the battery, starter, or chassis ground can interrupt power flow. Pay close attention to these points. Wiggle the cables gently while testing; a loose connection might show intermittent power.
* Ignition Switch: The ignition switch itself could be faulty and failing to send power to the rest of the system. This is a relatively common point of failure.
* Neutral Safety Switch: This switch prevents the starter from engaging unless the transmission is in Park or Neutral. A faulty neutral safety switch can cut power to the starter. (This wouldn't directly affect the instrument panel, though, making it less likely unless another issue is also present.)
* Starter Relay: This relay acts as a switch to deliver higher amperage to the starter motor. A failed starter relay will prevent the starter from engaging. You'll need to locate the relay (usually in a fuse box under the hood or inside the vehicle) and check it.
* Main Power Feed Wire: A break in the main power cable running from the battery to the rest of the vehicle's electrical system can affect everything. This wire is usually thick and well-insulated, but damage or corrosion can occur. This is more difficult to diagnose and often requires tracing the wire visually.
* Fuses and Circuit Breakers: Though less likely to affect *both* the starter and instrument panel simultaneously (unless it's a very large, overarching fuse), check the main fuses and circuit breakers in your fuse box(es).
* Alternator: While primarily for charging the battery, a completely failed alternator could result in a dead battery if the Blazer hasn't been run recently, leading to the symptoms you describe. A simple battery voltage test will quickly tell you if the alternator is working.
Troubleshooting Steps:
1. Battery and Cables: Start here! This is the simplest and cheapest check.
2. Visual Inspection: Carefully inspect all wires and connections for any visible damage.
3. Fuse and Relay Check: Check all fuses and relays related to the starter and ignition system. Consult your owner's manual for locations and ratings.
4. Voltmeter Test: Use a multimeter to test battery voltage, voltage at the starter, and voltage at the ignition switch. This will pinpoint where power is lost.
5. Ground Connections: Clean and secure all ground connections to the chassis and engine block.
If you're not comfortable working with car electrical systems, it's best to take your Blazer to a qualified mechanic. Incorrectly diagnosing and attempting repairs on the electrical system can lead to further damage or injury.
