Headlight Mystery Saga

[dogsridewith]

? Some kind of short and/or poor contact (high resistance) in the connector. (A poor contact makes heat, which melts plastic which lets things move and may start to sputter metal and/or let conductors touch and short.)
Also wondering about ground--if the ground leg becomes bad somewhere (wiring/connector/lamp-terminal), can the bulb holder or bulb base ground through metal or metalized plastic?
(A wiring short causes high amps...why fuses blow. A bad (high resistance) connection causes lower amps, but some of the energy (voltage x amps) gets turned into heat at the connection.)