reverse light switch, high resistance and leaks, why? Options

[davesprinkle]

OK, I'm now on my third reverse switch, with a consistent problem:

After a few hundred miles, the switch contacts become high-resistance (50 Ohms or so) and the switch leaks tranny fluid, filling up the wiring boot. By the way, the last two switches were brand-new Porsche replacements. I'm running Swepco 201, by the way. Anybody have any suggestions about what might be going on?

[jk76.914]

Well I installed my new switch from Pelican last weekend. The switch was sealed in a bag marked "Made in Germany", though there were no markings on the switch itself at all anywhere. (Maybe just the bag was made in Germany??).

So I installed the switch, and a brand new pin, and my backup lights worked properly. But the next day, I discovered they were on all the time! In any gear! So I removed the switch, and swapped the sealing washer with the one that was on the old switch. Tricky getting them off, but not too hard with big pliers. The old washer was about 3x the thickness of the new one. This thicker washer spaced the switch further out on the pin, and so now it's worked the way it should for over a whole week!

I was wondering why my original switch failed, so first I x-rayed both to see if I could make out any internal differences (old switch on the left, new one on the right). The plastic end of the switch, where the electrical connections are, is invisible in the x-ray.

You can make out a ghost of the sealing rings in the threaded butt of the switch, and see how much thicker the original one was compared to the new one.

Inside the switch is a rubber diaphram (I learned after cutting it apart- next photos). The rubber keeps the switch contacts separate from the transmission oil side of the switch, and stretches as the pin pushes the contact bridge up to mate with the two contacts on the connector pins.

Aside from the gasket thickness and the fact that the new housing is steel vs. the stainless of the old housing, they look like similar internal designs- except that the new one has an obvious metal dome under the contact bridge. The diaphram itself is invisible to x-rays, so it looks like that contact bridge is floating. This design for a switch or relay is called "bridging contacts". It requires 2x the contacts, is expensive, but it is the best way for high current situations, particularly with DC.



I took my old switch apart, and there was the contact bridge, two springs, and rubber diaphram. The contacts look like silver-cad-oxide, which are used for fairly high current and frequent makes-and-breaks. All in all, a very robust design. Zooming in on the contacts in the plastic housing, I think mine failed because of corrosion on the contacts. (Second photo)





So if I had it to do over, I'd start with both the thick and thin gaskets, with a new pin, and see if the switch closes. If it does, I'd leave it at that. If no, I'd remove the thin ring, and leave the thick one and try again. If no-go, then I'd remove the thick one and try the thin one. I'm guessing also that too much movement may stress that rubber diaphram and it may crack and leak with that thin sealing ring. Just a theory, and I'd be glad to x-ray and disassemble for anyone who has a switch that leaks through the terminals if you're interested to prove or disprove it.

Jim

[astronomerdave]

I was wondering why my original switch failed, so first I x-rayed both to see if I could make out any internal differences

Forget the switch, I want the x-ray machine. Too cool. I thought about building one when I was in school, but I presume you have access to this through work. What's the deal there?