Blowing Fuse 6

When rebuilding my VDO gauge pod I had the radio out and the steering column covers off. When I reassembled everything I was blowing fuse #6 every time I pulled the light switch.

Fuse 6 covers the right side parking lights, instrument lights, and license plate lights. On some cars it’s also the engine compartment light and rear foglight. Even though my car is Euro spec I’m missing those features. When the fuse blows I miss the instrument lights and the right side parking lights but not the turn signals or headlights. Annoying but not the end of the world.

I immediately suspected my wiring and gauge work. Could the small backlight bulbs in the gauges push the fuse over the edge with current draw? Possible since the previous owner didn’t have them lit so maybe it overwhelmed the system and he left them off. But this circuit should be able to handle additional lighting that I don’t have so that doesn’t make sense. I unplugged the gauge lighting ground anyway and the fuse still blew.

I wasn’t going to pull the instrument cluster without good cause so I searched elsewhere starting with the factory electrical wiring diagram for the switch.

“51” is the light switch schematic

Each circuit is labeled with a pin number but not its function. I had to trace through the diagram and the car to see where it each went. But doing this revealed which could be eliminated as the cause.

For example, anything with a brown wire is a ground. On this diagram I found Grey/Black is also a ground color code too. The second pin is also only activated at the switch’s 2nd position. That can only be the low beam lights (confirmed by tracing the diagram to the relay). Another is the 12v power input to the switch. That’s four of the seven circuits eliminated.

That left three circuits: the parking light wiring, one to the fuse, and one leaving the fuse to the instrument cluster lights. My electrical knowledge is limited here and I don’t fully understand the system but dumb luck narrowed it down even further.

I had pulled the light switch from the dash and left it hanging. I was checking connections and wires and blowing fuse after fuse until it worked. What changed? I had turned the dimmer all the way down to unscrew the headlight knob. Turning the dimmer back to full and the fuse blew. A bulb went off over my head!

If the fuse blows only when the dimmer is set to max the fault must be on a circuit affected by the dimmer. That eliminated the parking lights. And now it was down to the instrument cluster and the rest of the dash lights (including the VDO gauges).

I pulled the radio out again and the various harnesses spilled out again. Now I spent the time to do a better job of sorting each harness. And here I found a tiny harness with spade connectors left loose. The other end went to the cigar lighter. The spade connectors are not factory BMW so this is something the previous owner did. I looked but couldn’t find where it plugged into. With my voltmeter I checked and sure enough: at dimmer turned down there was 0 volts and at full brightness it was 11.8 volts. With it hanging loose it must have been shorting against the radio or the dash bar. And with it isolated from any metal I was no longer blowing fuses.

I couldn’t find where it went to. On my electrical diagram the white/blue color indicates it’s the automatic transmission (gear indicator) light. But my car is a manual – or was it originally an automatic? Or did the previous owner repurpose it for something else?

I tried to remove the cigar lighter to disconnect it but couldn’t get the lighter off the center console. I vaguely remember there is a trick to it but I wasn’t going to to go too far and break something. I ended up with capping off the live wire and taping it up.

Then I reassembled everything and took the extra time to better route the radio, climate control, and VDO wiring harnesses. When done I had solid fuses and good lighting all along the dash. Good, not great but that’s a project for another time.

Fuses for Troubleshooting

A note about these fuses. I knew I was going to be blowing more fuses as I tracked down the cause. No one really sells just the 8 amp white fuses in bulk. But I did find one supplier on Amazon with a 100-pack for $8.99. The only problem is they are slightly too long. I knew this ahead of time as the seller shows the length in the product info: 1” (25.4mm). The original fuses that I have are 19mm long.

Sure enough the new fuses are longer and maybe too long. They sit in between two spring-like tabs. It pushes the tabs apart even further and it’s impossible to tell if they will snap if I push them too far. But I went ahead and used them for my troubleshooting. I went through six of them without issues. But to avoid any potential problems I will get the proper sized fuse for long term use.

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