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?

[charliew]

Why not just put the tranny in reverse with the sw. out and measure how far the pin comes out and then press the sw. in that amount and see if it makes contact? If it doesn't see how far it needs to go in and adjust the sealing washers so it's not over pressing the bridge? The contacts will burn if the light ground is bad or the other connections are loose or dirty. Any high resistance connection means the complete circuit is carrying the aditional load and the contacts opening and closing will be arcing more and burning more.

[jk76.914]

Why not just put the tranny in reverse with the sw. out and measure how far the pin comes out and then press the sw. in that amount and see if it makes contact? If it doesn't see how far it needs to go in and adjust the sealing washers so it's not over pressing the bridge? The contacts will burn if the light ground is bad or the other connections are loose or dirty. Any high resistance connection means the complete circuit is carrying the aditional load and the contacts opening and closing will be arcing more and burning more.

When you increase the resistance in a circuit, the current flow is reduced, so I don't understand what you mean by "the complete circuit is carrying the aditional load and the contacts opening and closing will be arcing more and burning more."

Contacts tend to arc on opening, not closing. They may bounce on closing, and thus arc for an instant pending final closure. When contacts open, and arc, the arc ionizes the air between them, making it conductive, and thus allowing the arc to continue for longer than it would otherwise (like in a vacuum). Contacts switching AC last longer, because the current goes to zero 120 times per second (at least for 60hz AC) and self-extinguish. Contacts switching DC have to deal with the sustained arc. Worst case is DC switching an inductive load, which our light bulbs aren't. Solutions to all this are better contact material and bridging contacts like in our back-up light switches. Bridging contacts effectively open at twice the rate as single contacts, minimizing the opportunity for an ionization path to sustain an arc. The color of these contacts indicates to me that they are likely silver-cadmium oxide- low resistance, good thermal characteristics, and resistance to burning. As I said earlier- a very robust design.