[T3] DOT 5 and brake light switches

[Jim Adney]

On 4 Nov 2015 at 9:51, Sean Bartnik wrote:

> Keith, you bring up an interesting point. I guess the question is what
> kills the switches? Is it something chemical that is specific to DOT5
> that reacts badly with the materials in the switch? 

On the failed switchs I've cut apart, I've seen several with a melted 
plastic part, 1 with a defective internal part, and several with 
nothing that I can see. I haven't seen any sign of fluid leakage into 
the area where the contact is made, but that doesn't mean that 
there's no microscopic film there, that just doesn't happen to be 
visible.

On those latter switches, there must be an oxide layer that prevents 
conduction, but there's nothing visible. The corrosion could be due 
to external environmental causes, or it could be caused by an 
interaction between a bit of DOT-5 and the electrical spark that 
occurs when the contact is made or broken.

At this point I don't know. 

> If both, I might try wiring a relay into the circuit just as an
> experiment to see if switch life can be extended. 

I've considered doing that, with a relay or a transistor, but I 
really don't know if it would help. I haven't tried it yet. There's a 
set of 3 connectors in the trunk area that would be a good place to 
install something. It's important to understand that some kinds of 
contacts don't do well with only small currents. They need a minimal 
amount of current to keep the contacts clean.


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