Are there any connectors close to the light that are exposed to the weather, that's where I'd be looking first.
They could have corroded or the connector is loose, or a crimped connection to a plug or socket could require a drop of solder to improve the crimp, or the connector may need to be disconnected, given a bit of a blow out to get rid of dust and dirt that has made the socket and plug in the connection become 'dry'.
Regards, Marschy