Electrical circuits used in our Vanagons use copper wiring, with
connectors usually of brass. Both copper and brass as subject to
corrision (especially in the presence of water). As they corrode, less
metal is available to carry the electrical current (leading to higher
resistance in the circuit.) Higher resistance means that some of the
current goes into generating heat. Heat on wiring can lead to melting
of the insulation. This in turn can expose more of the wiring to
corrosion....

All of this takes time (and usually water).

I'm not positive as to what metal the fuses are made of, tin, aluminum
or something. I've seen surface corrosion on them as well.

With aluminum (and I believe tin), the surface oxidation tends to
prevent further corrosion. This is not true in the case of copper or
brass. However, aluminum oxide is a very poor conductor of electricity
and has a fairly high resistance (and remember that thing above where
resistance leads to heat?)

On Sep 30, 2009, at 1:16 AM, Rocket J Squirrel wrote:

> (If someone wants to chime in here with a description of how
> electrical
> bits in something simple like the brake light circuit can age in
> such a
> way that the on current is greater in an older van than in a new
> one, it
> would be helpful.)