If the button moves freely (spring works), the inside contacts will probably need cleaning. I'd try to take it apart and clean the contacts. I'm going to try it with mine, because they work sporatically.
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Prince Edward Island
'64 Parisienne CS "barn find" - last on the road in '86 ... Owner Protection Plan booklet, original paint, original near-mint aqua interior, original aqua GM floor mats, original 283, factory posi, and original rust.