* Burnt-out Bulb Filament(s): While you mentioned the tail light works, it's crucial to check the *bulb itself*. Brake and turn signals use separate filaments within the bulb. One or both of those filaments might be burnt out while the tail light filament remains intact. Replace the bulb with a new one; this is the cheapest and easiest fix.
* Bad Bulb Socket: The socket that holds the bulb might be corroded or damaged. Corrosion can prevent proper contact, leading to intermittent or no function for certain filaments. Inspect the socket for any signs of corrosion, damage, or loose connections. Clean it with contact cleaner if necessary. If it's damaged, replace the socket.
* Wiring Issues: A break or short in the wiring specifically for the left turn signal and brake light is possible. This could be due to wear and tear, rodent damage, or a previous repair gone wrong. Tracing the wiring from the bulb socket back towards the fuse box and turn signal switch is necessary, but requires some electrical knowledge and patience. You may need to look for exposed wires or broken connections.
* Turn Signal Switch: While less likely if the tail light functions, a failing turn signal switch could be at fault. It may not be sending the correct signal to the left turn indicator circuit.
* Fuse: While less likely given that the tail light works, check the fuse associated with the left turn signal and brake lights. A blown fuse would cut power to both functions. Consult your owner's manual to locate the appropriate fuse.
* Grounding Issue: A poor ground connection can interrupt the flow of electricity. A bad ground can cause intermittent or complete failure of electrical components. Check the ground wire connection at the taillight assembly.
Troubleshooting Steps:
1. Replace the Bulb: This is the *first* step. A new bulb is inexpensive and easily installed.
2. Inspect the Socket: Carefully examine the bulb socket for corrosion, damage, or loose connections. Clean or replace as needed.
3. Check the Fuse: Use your owner's manual to find the correct fuse and check its integrity.
4. Visual Inspection of Wiring: Carefully examine the wiring harness leading to the left taillight for any obvious damage or breaks.
5. Test the Wiring (Advanced): If you have some experience with automotive electrical systems, you can use a multimeter to test for voltage at the bulb socket when the turn signal and brake are activated. This will help pinpoint the location of the fault.
If you're not comfortable working with automotive electrical systems, it's best to take your Explorer to a qualified mechanic. Incorrect wiring repairs can lead to further damage or safety hazards.
