Industrial design nerdery: the VW-Hella accessory pull switch 211959621A

Lightbulb removal
Hella 211959621A pull switch - lit
211959621A diagram bitmap

It's sturdy, it's got a touch of german, 60s-70s industrial design. Yes, I'm talking about one particular VW part, the pull switch used in the '68-'79 kombi in a couple of varieties, this one is green and controls the rear window defogger.

In our bus the defogger is currently decommissioned, and among the small mysteries which are revealed when exploring the bus I found this switch hanging by a couple of wires under the dashboard. It wasn't hooked up to anything in particular, and the green lens was covered up in deep scratches to the point where the defogger symbol was no longer recognizable.
Later, when I started work on the electrical system (a major one-step-at-a-time overhaul), I removed the suspending cables and decided I might as well put the switch into use as bypass for the car's sound system (up to this point we'd manually connected the wires when we were in the mood for some beats).

The basic design is a pretty nifty one for its intended use (automobiles): it's big and grippable – still the space it occupies is comparable to a flip-switch. Once you get used to the convention that pull (out) equals on, you can maneuver it without looking. This makes it safe & easy to shut everything down by just pushing all the dashboard knobs. It's also a lesser evil in the case of a collission, the knob is made of semi-soft rubber and it's just one bulbous part sticking out of the dashboard which won't hurt you particularly if you're thrown against it. And finally, it has a nice, comfy glow when the light is lit in the 'on' position.

As shown in the diagram there are three connectors:

  1. + input
  2. ground (for lamp)
  3. + switched

Electrically, 1 and 3 are interchangeable since closing the circuit makes a connection between the lamp and the switched circuit. The assembly consists of four parts including the lightbulb:

  1. base
  2. shaft with bulb socket
  3. bulb
  4. colored lens

The lightbulb is a bit curious, it's not among the more common auto light bulbs. The form factor is conveniently called w2,1x4,6d. Since there is no metallic base, you might be fooled into thinking it's broken if you find one lying around (as I did). The VW part no. is N 017 751 2 which corresponds to Osram 2721. Replacement bulbs are special order but not that hard to find (links below), and there are LED substitutes available as well. In my case, the switch I was going to use had a burnt-out bulb. Earlier however, I had noticed what I thought was a broken tiny lightbulb lying around in a groove in the bus flooring. Turned out it was one of these, and a working one too!

Bulb replacement

The lens unscrews, revealing the lightbulb in a recess not quite fit for grabbing with unaided fingers. Before you go grab some pliers, let me remind you that this is a tiny, precision-made glass bubble which means that it's very fragile and at the same time crazy slippery. I tried a couple of ways of pulling the bulb out to no avail. At least I didn't break it, which probably would have made things worse since there would be even less left to grab – those of you who've dealt with grownup-size lightbulbs stuck in their sockets know what I mean!
Turns out, the best (and probably intended) way of removing the bulb is by pushing from the back: unscrew the shaft, then find a sewing needle as wide as will still easily slide into the little hole in the threaded bottom of the shaft. Run the blunt (eye) end of the needle into the hole 'til it hits the bottom of the bulb. Using a suitable surface to rest the sharp end on, push as hard as needed until the bulb pops out of its socket.
Fitting a new bulb is ridiculously easy by comparison. The only thing to keep in mind is to check beforehand that the bulb is working, considering the labor of removing it again once it's hooked up back in the car.

Links

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This image, Hella 211959621A diagram, by Arvid Rudling is licensed under a Creative Commons Attribution-ShareAlike 2.5 Sweden license.

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