Ignition Switch and Wiring Test – 2.5L NA

Overview

This procedure tests the ignition switch and its wiring to the starter on a Porsche 944 (8-valve engine) to diagnose starting issues. A faulty ignition switch, often indicated by cracks, can prevent the car from cranking. This guide covers both pre-1985.5 and 1985.5 onwards models, with no model-specific differences noted in the original procedure.

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Tools Required

• Wire jumpers
• Multimeter

Parts Required

• Ignition switch (if replacement is needed): 944 610 911 00
• Wire, Red with Black Stripe (if replacement is needed): 999 701 013 50

Step-by-Step Procedure

Step 1: Disconnect the Battery

1. Locate the battery in the engine compartment (front of the vehicle).
2. Using a 10mm (3/8 inch) wrench, loosen and remove the positive battery cable from the battery terminal.
3. Secure the cable away from the battery to prevent accidental contact.

Step 2: Access the Ignition Switch

4. Locate the ignition switch behind the steering column, accessible from under the dashboard.
5. Disconnect the electrical plug from the ignition switch by gently pulling it off.

Step 3: Test the Ignition Switch

6. Identify Terminals 30 and 50 on the ignition switch electrical connector. Terminal 30 connects to the large-diameter Red Wire, and Terminal 50 connects to the large-diameter Red Wire with Black Stripe.
7. Connect the probes of a multimeter set to resistance (ohms) mode between Terminals 30 and 50.
8. Turn the ignition key to the start position, as if cranking the engine, and observe the multimeter reading.
9. Verify that the resistance drops from infinite to approximately 0 ohms when the key is in the start position.
10. If the resistance does not drop to approximately 0 ohms, the ignition switch is faulty and should be replaced with a new ignition switch (944 610 911 00).

Step 4: Test the Ignition Wiring

11. Locate the starter solenoid under the car, near the transmission.
12. Disconnect the Red Wire with Black Stripe from the switch terminal on the starter solenoid.
13. Create a jumper wire long enough to reach from the starter solenoid to the ignition switch electrical connector.
14. Attach one end of the jumper wire to the Red Wire with Black Stripe at the starter solenoid.
15. Attach the other end to the terminal on the ignition switch electrical connector that corresponds to the Red Wire with Black Stripe.
16. Use a multimeter set to resistance mode to measure the resistance through the jumper wire and the Red Wire with Black Stripe.
17. Verify that the resistance is approximately 0 ohms (less than 5 ohms).
18. If the resistance is higher than 5 ohms, the Red Wire with Black Stripe is faulty and should be replaced with a new wire (999 701 013 50).

Post Procedure Checklist

• Ensure the ignition switch electrical plug is securely reconnected.
• Verify the battery positive cable is reconnected and tightened to 10 Nm (7 ft-lbs) using a 10mm (3/8 inch) wrench.
• Check that all tools and debris are removed from the work area.
• Test the ignition by turning the key to the start position to confirm the engine cranks properly.
• Inspect the ignition switch visually for cracks or damage, even if it tests okay, as cracks may indicate future failure.

Sources

• Clark’s Garage
• Pelican Parts
• Porsche 944 Workshop Manuals
• YouTube