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Re: Harness Conductivity

On  3 Dec 97, T. A. Dapper wrote:

> Jim
> The connectors on these cars are all crimped in place.  If the metal in
> the connector is not identical to the metal in the wire, can you not get
> electrolysis and end up with corrosion or at least resistance between
> the wire and the connector?

With dissimilar metals in the presence of an electrolite you can get 
galvanic corrosion, but the effect is not strong between copper and 
the brass terminals, and it is nonexistant in the crimp itself since 
the crimp excludes the electrolite and air necessary for this action.

Even the push on connectors will form a gas-tight seal in the 
(small) contact area as long as they have not been abused and 

> If the climate is humid and salty, can you not have corrosion between
> the wire strands themselves? 

There would not be any galvanic corrosion, and any other kind would 
require the continuous addition of some reageant (sp?) to react with 
the copper.

 I believe that seven individual strands
> are not as conductive as seven strands twisted together, touching along
> their length.

I don't see why, as long as none of the strands are broken.  At high 
frequencies the opposite is actually true, but we are talking DC, or 
nearly so, here anyway.

  A break in the insulation can allow a corrosion point.
> Heat felt at such a point indicates resistance, and a lessened current
> flow.

I don't think I have ever seen an example of this.  I would expect it 
to be the result of broken strands, probably caused by someONE, 
rather than by a chemical process.

The kind of thing that CAN happen is that you have a nick in the 
insulation in an area where the wire sits in a pool of water long 
term.  Then the water forms an electrolite with road salt and you get 
galvanic corrosion between the copper in the wire and the iron of the 
car body.  I hope you'll agree that this is a rather extreme 

Another problem that happens is where you have contact spread over a 
rather large area like under the 8mm nut on the starter.  The area 
there is large enough that the pressure is not high enough for the 
joint to be gas-tight, so over time the surfaces can oxidize and 
become insulating.
> However, I agree that bad connections and contacts are the biggest
> contributors to harness problems in an old Type 3.

I would add human contributing factors to the list.

       Melissa Kepner                                    Jim Adney
                             Laura Kepner-Adney
                             Madison, Wisconsin

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