* Reverse Light Switch: This is the most frequent cause. The switch is mechanically linked to the transmission and activates the reverse lights. If the switch is faulty, it might be shorting the electrical system, creating a load that interrupts the ignition circuit. The switch can be worn, corroded, or simply misadjusted.
* Wiring Issues: Poor connections, frayed wires, or corroded terminals in the reverse light circuit can cause interruptions. These problems can disrupt the current flow, potentially affecting the ignition system. Check the wiring harness near the transmission and the reverse light switch itself.
* Ignition Switch: While less likely to be the direct cause, a worn or faulty ignition switch can sometimes exhibit strange behavior under load, like when engaging reverse.
* Solenoid Issues (Less Likely in a '72): While later Beetles had electric solenoids for the starter, a '72 likely uses a more mechanical system. However, if there's some interaction between the starter and reverse gear engagement (e.g., a binding issue), it could indirectly affect the ignition.
* Ground Issues: A poor ground connection somewhere in the electrical system can cause all sorts of problems, including intermittent shutdowns.
Troubleshooting Steps:
1. Check the Reverse Lights: Do your reverse lights even come on when you put the car in reverse? If not, the problem is almost certainly the reverse light switch or its wiring.
2. Inspect the Reverse Light Switch: Locate the switch (it's usually on the transmission). Look for corrosion, loose connections, or physical damage. Try gently moving it to see if the contact is intermittent. This might require some investigation under the car. Replacing this switch is relatively inexpensive and easy.
3. Examine the Wiring: Carefully trace the wiring from the reverse light switch to the lights themselves, and also to the main wiring harness. Look for any signs of damage, corrosion, or loose connections. Clean any corroded terminals with a wire brush and electrical contact cleaner.
4. Test the Ignition Switch (if other steps fail): This is more involved and might require some electrical testing with a multimeter.
5. Check Ground Connections: Ensure the battery is properly grounded, and check other ground points throughout the car's electrical system, particularly around the engine and transmission.
Important Note: Working on your car's electrical system requires some basic knowledge and caution. If you're not comfortable working on car electrical systems, it's best to take your Beetle to a qualified mechanic, especially given the age of the car. Improperly working on the electrical system could cause further damage.
