[T3] Brake Lights

Jim Adney jadney at vwtype3.org
Wed Jul 6 04:45:25 PDT 2011


On 5 Jul 2011 at 14:38, Bryon Garvin wrote:

> It seems to to *mostly* be the same diameter all the way thru the threads.
>  Possibly near the end, it looks to widen out and maybe that's too soon?  I
> threw the rest of the switch away days ago so I don't have it to compare
> with the threads anymore.  But I can tell you that the switch body had about
> a 3/8" hole where these threads would mate up.  So, clearly, it broke at the
> point where the hole widened to meet the switch body.

A 3/8" step bore would certainly create a weak spot in a bad place. 
The people who make these should understand this and there's no 
reason to do it this way. Nevertheless, it seems to be a common 
mistake. I suspect it comes from a design that worked fine as a 1/4" 
and 3/8" NPT and was then simply modified into the 1/8" NPT and 
tapered 10 mm.  

> I did notice that once the threads were missing, the diaphragm was easily
> seen.  I used a screwdriver to push on it and checked the pins with a
> multi-meter.  Part way down, the first contact was made which I assume is
> the circuit that would operate the brake warning light.  Pushing further,
> the next contact made operated the brake lights.   So it was 2 stages which
> I thought was interesting.

The warning light is the NC contact. As you apply pressure, that 
contact opens, then the NO contact closes.

> BTW, do you need to use a thread sealing compound on these switches?  I have
> seen the ones that do have it on there right out of the box.

I find that they seal okay without any help. That's what the tapered 
thread does.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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