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Electric current from the controls on car steering wheels passes through
sliding contacts. When the contacts get dirty or wear out, the level of the
signal can drop and the controls may fail. To get round this, TRW of California
proposes using different frequencies to carry the signal, rather than changes in
voltage or current (EP 1020331). Even if a signal is muffled by dirt or wear,
its frequency remains the same and the message gets through. This should make
your turn indicators more reliable, it argues.