VW Beetle Terminal 30 Starting Issues & Fixes

I faced a very similar issue with my 2012 VW Golf, which has almost identical electrical architecture to your Beetle. With some experience working on VW electrical systems, I can share what worked for me. The symptoms you describe match exactly what I encountered, weak cranking despite a seemingly good battery voltage. After bringing it to my workshop, they found the charging system was not properly maintaining the battery charge due to a deteriorating wiring harness near the alternator. The constant drain was causing starting issues even though the battery showed acceptable voltage when tested. The repair involved: Complete charging system diagnostic, Replacement of corroded wiring harness sections, New battery terminals, Circuit breaker inspection, Fuse box connection cleaning Total repair cost was 290€ which included parts and labor. Before suggesting specific solutions, could you share: Has the check engine light been on? Do you notice dimming headlights? When was the last battery replacement? Have you checked alternator output voltage while running? This information would help determine if your issue stems from similar root causes. The Terminal 30 circuit on VWs often develops issues where the wiring harness connects to the fuse box, which can cause the symptoms you describe.

Latest service completed at 103000km. The suggestion about the charging system connection makes sense. After checking further, I found corrosion buildup at the battery terminals and a noticeable voltage drop when testing the circuit between the alternator and battery. A voltage test showed: Battery at rest: 12.6V, During cranking: Drops to 9.8V, Running engine: 13.7V The ignition switch also feels loose when turning the key. Would checking the wiring at the fuse box connection points be a good next step before replacing parts? The 290€ repair cost seems reasonable if it resolves these starting issues completely. I might also need the circuit breaker tested since theres an occasional clicking sound from that area during start attempts.

Having gone through nearly identical issues with my VW Golf, those voltage readings definitely point toward what I suspected. The voltage drop to 9.8V during cranking is concerning, on my car, this was a clear sign of resistance in the wiring harness connections. The loose ignition switch combined with the clicking from the circuit breaker area suggests multiple points of electrical fault in the starting circuit. When I had my car repaired, they found that the starter motor was getting insufficient power due to degraded connections at both the fuse box and near the alternator. Looking at your voltage readings and the corrosion you found, you seem to be dealing with the same charging system problems I experienced. The 13.7V while running is borderline acceptable, but combined with the deep cranking drop, it indicates resistance in the circuit. I would strongly recommend: 1. Having the entire wiring harness inspected, especially near heat sources 2. Testing the circuit breaker and starter motor draw 3. Cleaning or replacing corroded terminals 4. Checking all ground connections The clicking sound you mention is exactly what I heard before my repair, it turned out to be the circuit breaker responding to voltage fluctuations from the compromised wiring. The short circuit protection system might also be engaging due to the resistance in the charging system, which explains the multiple start attempts needed.

Thanks for sharing your experience with a similar VW Golf electrical issue. Your findings about the wiring harness connections actually match what I'm seeing. The voltage readings from my tests make more sense now, especially that 9.8V drop during cranking. After inspecting more closely based on your feedback, I found additional corrosion under the fuse box cover and noticed the power supply cables are showing wear near the alternator mount. The starter motor also draws more current than spec according to my multimeter test. I'll schedule the repair work next week focusing on: Complete wiring harness inspection, Circuit breaker replacement, Cleaning all ground points, Testing the starter motor, Checking for any short circuit conditions The 290€ estimate seems fair considering the electrical fault diagnosis and parts needed. I really appreciate the detailed explanation about how the charging system and ignition switch problems connect to the starting issues. Will update once the repairs are completed. Good call on checking those circuit breaker connections too, that clicking sound during starting attempts definitely indicates it needs attention.

What is terminal 30?

(Translated from German)

Terminal 30 refers to a constant power supply in a vehicle's electrical system, typically connected directly to the battery. It provides continuous power to certain components, even when the ignition is off. If there's an issue with Terminal 30, it can affect the vehicle's ability to start or maintain electrical functions. If you suspect a problem with Terminal 30, check for loose connections, corrosion, or damaged wiring. Let me know if you have any further questions!