* Wiper Switch: The switch itself could be faulty. Internal contacts might be sticking or shorted, allowing power to reach the motor regardless of the switch position. This is a common failure point in older vehicles.
* Wiper Motor: The motor itself could have a short circuit within its windings. This is less likely to cause intermittent operation, but it's possible a failing component inside the motor is causing it to sporadically activate.
* Wiring Harness: A short in the wiring harness leading to the wiper motor is a strong possibility. Wires can fray, melt, or become pinched, creating an intermittent connection that allows power to flow erratically. Look for damaged insulation or areas where wires might be rubbing against metal. Pay close attention to the area around the steering column and firewall.
* Park/Intermittent Timer Relay (or related components): The system uses a relay or timer circuit (often a resistor) to control the intermittent wiping speed. A malfunction in this circuit could be causing the intermittent function to operate unexpectedly. It's possible the relay is sticking or has an internal short. This component is crucial for controlling the off state.
* Ground Connection: A poor ground connection in the wiper motor circuit can cause erratic behavior. A corroded or loose ground wire can lead to intermittent activation and other electrical gremlins.
Troubleshooting Steps (in order of easiest to hardest):
1. Check the Wiper Switch: See if you can carefully inspect the switch itself (after disconnecting the battery's negative terminal!). Look for any obvious signs of damage or corrosion. Often, wiggling the switch while observing its behavior can reveal if a bad connection is the problem.
2. Inspect the Wiring Harness: Visually inspect the wiring harness from the switch to the wiper motor, paying attention to areas prone to wear and tear. Look for any exposed wires, frayed insulation, or areas where the wires might be pinched or grounded against metal.
3. Check Ground Connections: Locate the ground wire for the wiper motor and ensure it's clean, tight, and well-connected. Clean the ground point with a wire brush if necessary.
4. Test the Wiper Motor (with caution!): If possible, test the motor directly with a multimeter (after disconnecting power and confirming continuity) to see if it's drawing power even when it shouldn't be. This should be done by a professional unless you are very comfortable working with automotive electronics.
5. Relay/Timer Circuit: This will require more advanced diagnostic techniques to identify and test the related components. This usually requires schematic diagrams to trace the circuit and test the various components with a multimeter.
Important Safety Note: Always disconnect the negative battery terminal before working on any electrical components in your vehicle to prevent short circuits and electrical shocks. If you're not comfortable working with automotive electrical systems, it's best to take your Astro to a qualified mechanic for diagnosis and repair.
