Galvanic corrosion question

[reggiemon]

For the experts. Galvanic corrosion question
I have black areas around all of the exterior lights as well as hinges, etc. How do I make sure the corrosion is stopped?
Can I just clean these spots & leave them or should I coat them with something?
I am putting neoprene gaskets under the steel tail light, license plate housings. The marker lights are new with alum bases. Do I coat the gaskets/bases with vulkem to completely seal the surface?
I would appreciate any advice!

[markdoane]

I'm not sure what you have. Most aluminum corrosion products are gray or white, so don't know how to interpret the black. Is it possible the black is dirt?

If you try to polish a small area, you will get lots of black material, but that's not from galvanic corrosion.

Sorry to be so difficult, but the answer depends on the correct diagnosis.

[hampstead38]

I suspect black areas are not oxidized aluminum... which as Mark points out, is normally gray. When I pulled the marker lights on the '67 Overlander, there was some dark material which I presumed was aged sealant or perhaps the remnants of rubber grommets.

If you are attached aluminum bases to an aluminum skin using aluminum rivets, galvanic corrosion should not be an issue. To maintain maximum sealing, I think many folks use Vulkem. In doing my marker lights, my concern was less corrosion and more leakage.

Before you cover the bases completely, you might want to think about grounding. I think most marker lights are grounded to the skin/frame rather than having a dedicated ground wire. You don't want to do such a good job of sealing with Vulkem that you eliminate the ground necessary for the lights to function.

[reggiemon]

Thats OK. I will take pictures if needed.
After polishing, the areas around the light fixtures have black stains that are rough and you cannot polish the black area out. It does not show up in pictures well. I just want to make sure nothing will continue to deteriorate. I had some white powder under the tail light assy as well as the black stained areas.
All the lights are grounded to the skin. I do wish I could run seperate ground wires to all the fixtures but do not want to pull any inner panels off.

[Woody.303]

Aluminum and steel don't get along.

If you have an area where aluminum and steel are touching each other, add a little bit of water, and you will have corrosion. The water can be from humidity in the air.

Auto manufacturers are still trying to learn this lesson.

Use plenty of Vulkem to separate the two dissimilar metals, or a rubber gasket. This may require running new ground wires. Sorry to be the bearer of bad news.

Woody