1. Check the Wiper Switch Stalk:
* Visual Inspection: Carefully examine the wiper switch stalk. Look for any obvious signs of damage, broken wires, or corrosion. Pay close attention to the connections at the back of the stalk where it plugs into the steering column. Loose or corroded connections are a common culprit.
* Testing (Advanced): If you're comfortable with electrical testing, you can use a multimeter to check for continuity and voltage at the wiper switch connections. This requires a wiring diagram specific to your 1999 Isuzu Rodeo to identify the correct wires. A wiring diagram can often be found online (search for "1999 Isuzu Rodeo wiring diagram") or at a parts store.
2. Check the Wiper Motor Resistor (if applicable):
* Location: The intermittent wiper resistor is often located somewhere under the dash, near the wiper motor, or sometimes even within the wiper motor assembly itself. You'll need to consult your vehicle's repair manual or an online parts diagram to locate it precisely.
* Testing: If you find the resistor, you can test it with a multimeter to check for continuity and resistance. A faulty resistor will often show an open circuit or incorrect resistance value. *However, many newer vehicles don't use a separate resistor, but rather control the speed through the wiper control module.*
3. Check the Wiper Control Module (most likely culprit):
* Location: This is a more complex component that might be integrated into the wiper switch stalk itself or a separate module under the dash. Again, consult your repair manual for the exact location.
* Testing & Replacement: Testing a wiper control module is often difficult without specialized equipment. If you suspect it's faulty (and you've ruled out other causes), replacement is usually the most practical solution. You can find replacement wiper control modules at auto parts stores or online retailers. *Be sure to get the correct part number for your specific vehicle year and model.*
4. Wiring Harness:
* Check the wiring harness for any breaks or shorts between the wiper switch, resistor (if present), and the motor.
Troubleshooting Steps:
1. Start with the easiest: Begin by checking the wiper switch stalk for loose connections or damage. This is the most common and easiest fix.
2. Consult a repair manual: A repair manual specific to your 1999 Isuzu Rodeo is invaluable. It will have wiring diagrams, component locations, and troubleshooting guides.
3. Visual Inspection: Thoroughly inspect all components involved in the wiper system before resorting to electrical testing.
4. Professional Help: If you're not comfortable working with automotive electrical systems, it's best to take your vehicle to a qualified mechanic.
Important Note: Safety first! Disconnect the battery negative terminal before working on any electrical components in your vehicle. Incorrect wiring or short circuits can damage your vehicle's electrical system or even cause a fire.
