* Faulty bulb: Although it's unlikely that both the turn signal and marker light filaments in the same bulb would fail simultaneously, it's still worth checking. Replace the bulb with a known-good one and see if that resolves the issue.
* Corrosion or damage to the bulb socket: The bulb socket may be corroded or damaged, preventing good electrical contact between the bulb and the socket. Check the socket for any signs of damage and clean it if necessary. You can use a wire brush or electrical contact cleaner to clean the socket.
* Faulty wiring: There may be a problem with the wiring between the bulb socket and the turn signal/marker light switch. This could be due to a loose connection, a broken wire, or a short circuit. Check the wiring for any signs of damage or loose connections and repair or replace as necessary.
* Faulty turn signal/marker light switch: The turn signal/marker light switch may be faulty, preventing power from reaching the bulb socket. Try actuating the switch several times to see if that makes the marker light come on. If not, the switch may need to be replaced.
If you're not comfortable performing these checks or repairs yourself, it's best to take your vehicle to a qualified mechanic for diagnosis and repair.
