VW 12V Testing

Today I took a closer look at the Beetle’s 12V electrical system. Using a bench power supply with 12.5V and 8A (also tested at 12.8V), I ran a preliminary test to see what would come alive and to check for any unexpected current draw. Even with nothing on, the system drew only 0.060A, which is within normal limits and indicates no major shorts.

I spent a while trying to figure out how to test the 12v system without an ignition key. I’m probably on a list for the things I googled. I couldn’t turn the key, so I assumed that the door and ignition keys were no longer a match (and I only had one), but it turns out, the key was upside down (doh!). It’s a lot harder to put in from that direction but once in, it turned easily.

Once the key was turned, several systems came online:

• CD/MP3 player powered up and made CD loading sounds (the display was garbled, I’m not keeping it anyway)
• Hazard lights worked on the left front, left back, and front right
• Headlights did not come on, but the blinkers came on when the headlight switch was turned to the first position
• Blinker and hazard lights had an odd cycle: they would start with the turn signal sound, fade, then return intermittently. This is likely due to the thermal flasher unit, which may not be functioning correctly without a full load.
• Fan worked on all three speeds (a welcome surprise)
• Ignition made a click (with no starter motor installed, this was just the solenoid)
• Brake lights did not illuminate (a couple wires got disconnected during the engine drop, I’ll need to fix that)
• Windshield wipers functioned, but moved very slowly (I’ll likely need to replace the wiper motors)

Overall, this is very encouraging. There are no major electrical faults, and the minor sluggishness is almost certainly due to the bench power supply, which isn’t capable of delivering the bursts of current a real car battery provides. The bench supply is a good safety check–a full car battery could deliver hundreds of amps in a short circuit, which could be dangerous if there were any wiring issues.

Next steps will be to test the system with an actual 12V battery to see everything operate under normal load. One upgrade I’m considering is replacing all the exterior bulbs (blinkers, headlights, tail/brake, and reverse) with LEDs in the long run. This change alone would reduce the system’s current draw from ~15–20A down to ~3–5A. I will also need to replace the thermal flasher with an electronic one to ensure reliable blinking with LEDs.

All in all, this was a successful safety and functionality test–a solid foundation for moving forward with the EV conversion. It also gave me something to do while waiting for parts to arrive.