* Wiring harness issues: This is the most likely culprit. A frayed wire, chafed insulation rubbing against metal, or a corroded connection within the 4x4 system's wiring harness can cause a short. Inspect the wiring from the 4x4 switch to the actuator motor(s) and related components very carefully. Pay close attention to areas where the harness might rub against metal parts.
* Actuator motor problems: The motor that engages the 4x4 system (transfer case actuator or shift motor) could be drawing excessive current due to a malfunction. A seized or damaged motor will try to draw far more current than it should, blowing the fuse.
* Switch itself (even a new one): While you've replaced the switch, there's a small possibility the new switch is faulty or improperly installed. Double-check the installation and consider testing the new switch with a multimeter to ensure it's functioning correctly.
* Transfer case issues: Problems within the transfer case itself can sometimes cause excessive current draw. While less likely, it's possible there's a mechanical issue that's putting extra strain on the actuator motor.
* Other components in the 4x4 system: There could be problems with other components like the shift motor, speed sensor, or related circuitry.
Troubleshooting Steps:
1. Visual Inspection: Thoroughly examine all wiring related to the 4x4 system. Look for any signs of damage, corrosion, or fraying. Trace the wires from the switch to the transfer case actuator motor.
2. Continuity Test: Use a multimeter to check the continuity of the wiring harness. Disconnect the wiring harness at both ends (switch and actuator) and test for continuity in each wire. Any breaks in the circuit will indicate a damaged wire.
3. Actuator Motor Test: If the wiring checks out, the next step is to test the actuator motor itself. This might require removing the motor for easier access and testing (consult a repair manual for specifics).
4. Transfer Case Inspection: While less likely, a mechanical issue in the transfer case can affect the motor's operation. This is a more involved diagnostic step that might require professional help.
Important Note: Before conducting any electrical tests, disconnect the negative battery terminal to prevent accidental shorts and potential damage. If you're not comfortable working with car electrical systems, it's best to take your S10 to a qualified mechanic. Improper electrical repairs can lead to further damage or even fire.
