1. Diagnosis: Isolate the Problem
Before diving into repairs, accurately pinpoint the problem. Several things can go wrong:
* Power Issue: The mirror might not receive power at all. Check the fuse (consult your owner's manual for the correct fuse) and the wiring harness leading to the mirror. Look for broken wires, loose connections, or corrosion. A multimeter can help verify power reaching the mirror's motor.
* Motor Failure: The mirror motor itself may be burnt out or seized. This is the most common failure. You'll likely need a replacement motor.
* Switch Failure: The power window and mirror switch assembly might be faulty. Sometimes, just cleaning the switch contacts can fix intermittent problems. If the switch is bad, it will need replacement.
* Gear Failure (Less Common): The gears inside the mirror assembly that drive the movement might be stripped or broken. This usually results in the mirror not moving smoothly or at all. Often, this requires a complete mirror replacement.
2. Repair Process (based on diagnosis):
* Power Issue:
* Check the fuse: Replace the blown fuse if needed.
* Inspect wiring: Carefully examine the wiring harness running from the switch to the mirror. Look for breaks in the insulation, frayed wires, or corrosion at the connectors. Repair or replace any damaged wiring.
* Test for power at the mirror: Use a multimeter to check for power at the mirror connector. If no power, trace the wiring back towards the switch and fuse.
* Motor Failure:
* Access the mirror: This usually involves removing the door panel (there are many online guides and videos specific to 1991 S-10 Blazers showing how to do this).
* Remove the mirror assembly: Once the door panel is off, you'll typically need to disconnect the wiring harness and remove the mirror assembly itself.
* Replace the motor: The motor is usually replaceable. You'll need to source a replacement motor (from a junkyard, parts store, or online). Carefully remove the old motor and install the new one.
* Switch Failure:
* Access the switch: Locate the power window and mirror switch assembly (often on the driver's side door panel).
* Clean the switch (try first): Sometimes, contact cleaner can restore function to a dirty switch.
* Replace the switch: If cleaning doesn't work, the switch will need replacement. It's often sold as a single unit.
* Gear Failure:
* This is generally the hardest to fix. Often, replacing the entire mirror assembly is the most practical solution.
3. Parts Sourcing:
* Junkyards: A great place to find used, working parts cheaply.
* Auto Parts Stores (e.g., AutoZone, Advance Auto Parts): Can supply new or remanufactured motors and switches.
* Online Retailers (e.g., Amazon, eBay): Offer a wide selection of parts.
Important Notes:
* Disconnect the battery negative terminal before working on any electrical components.
* Consult a repair manual: A Haynes or Chilton repair manual specific to your 1991 Chevy S-10 Blazer will provide detailed diagrams and instructions. These are invaluable for removing door panels and accessing the mirror assembly safely.
* YouTube Videos: Search for "1991 Chevy S-10 Blazer driver side mirror repair" on YouTube. You'll likely find helpful videos demonstrating the process.
Remember safety first. If you're not comfortable working on car electrical systems, it's best to take your Blazer to a qualified mechanic.
