Automotive electrical contacts

  1. Hi,
    I had auto lights failing and instead of let the mechanics supply me with a brand new switch unit at a great rate, I delved into the switch unit to see what was happening.
    I noticed a lot of oil and grease in the box containing the switches. The contact plates were covered in the grease, some blackened with friction over time. The grease looked like it had transformed to an oil in places and had run over the insides of the box a little. I noticed the lever contact was rough and was gouging a deep scrape in the contacts. I sanded the problem areas to smooth and allow them to work more regardless of the groove.
    I fixed the problem.
    Then, on a cold night, the lights failed to work again.
    I wonder if it's the grease that's getting old, is solidifying a little and more so in the cold and stopping the contact in the switch.
    So have a couple of questions.
    1/ What type of grease is it that they use in electrical auto switch components, that stops friction but allows electricity to pass well? or should you use grease in electrical switches for that matter?
    2/ Is there an inexpensive, hard friction resistant electrical conductive product that could be applied to the gouge in the brass/copper (not sure what it is?) contact plate to make it smooth/flat like it was? Solder wouldn't be hard?, Epoxy products? other? Something to fix it like new without having to fabricate a new contact plate.
  2. jcsd
  3. Danger

    Danger 9,663
    Gold Member

    The temperature might well have something to do with it, but I'm not so sure that it's because of the grease stiffening up. If the wear in the switch was sufficient (particularly after you sanded it), the metal might contract enough in the cold to break contact. Try taking a hair dryer to the switch with it turned on but not conducting, and see if the lights come on.
    As for building up the switch, a hard solder might be durable enough. I'd recommend against brazing with all that flammable stuff around.
    I would suspect that the grease is either lithium-based or moly disulphide. Both are suitable for winter use in most locations.
  4. No, the switch contacts are not avoiding eachother in any way and one is sprung sufficiently to contact. The only thing that can be between them is that grease.
    So do all greases allow electricity to pass, or are there special ones specifically for that purpose?

    I will of course keep your suggestion in mind when I next disassemble the component, just in case!
    Last edited: Dec 3, 2007
  5. The grease is there to prevent oxygen and moisture in the atmosphere from getting getting on the switch contacts when they are closed. When a slight voltage is built up across a connection (impossible to avoid since no switch is perfect) moisture or oxygen can cause corrosion to start. The grease may very well have aged and become stiff to the point that the contacts cannot completely squeeze it out of the way when they close. As to what to replace it with? Not sure. Try google.
  6. dlgoff

    dlgoff 3,158
    Science Advisor
    Gold Member
    2014 Award

    You might try just getting rid of the "grease". I would flush it out with methanol or some mild solvent. Then see if it works.
  7. Danger

    Danger 9,663
    Gold Member

    WD40 would work pretty well for removing the grease, and helping to keep the contacts dry. I agree with ASN that there might be a very thin layer of hardened grease in the way if it indeed looks to you as if there is contact.
    Just as a side-note... no offense intended, but are you sure that the problem is in the contact interaction area? Could it maybe be a loose connection between the contacts and the wiring harness, for instance? That could suffer from the same thermal contraction that I mentioned in regard to the contacts earlier, and might be hard to see.
  8. brewnog

    brewnog 2,775
    Science Advisor
    Gold Member

    Don't be such a tightarse, get a new switch.
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