I get the 'one honk/one light flash' issue sometimes as well. I'm not sure what the issue is but sometimes just opening the drivers door fixes the problem, sometimes opening and closing the console or glove compartment does it. I'm guessing I'll have to try and get at all the contacts for the microswitches and try and clean and/or replace them.
My center console does it every so often, in fact it did yesterday! Closed it firmly, no more honk
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2001 Boxster S Lapis Blue
TS Cat Bypass Pipes and exhaust
iPad Mini Dash Install
DEPO Tail Lights