It sounds like to me more of a bad connection than a short, I would check and clean the light sockets, make sure your getting a good connection to the bulb. Shorts dont typically come and go. If you have an ampmeter you could check the current draw of the circuit, its also possible the breaker is weak and tripping with nothing wrong with the lights at all.
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Jeff
'14 Cruisers 380 Express "Simon Sez"
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