Toyota Trucks: 1994 4 runner brake lights

Brake lights work normally during daylight operation. When headlights
are turned on however, one brake light fails to illuminate when pedal
pushed. Does anyone know what may be the cause? Bill

Joseph Wind wrote: 

Might also check the power and ground connections at the light socket. I've seen cases where these dual filament lights work fine one light on or the other, but not both. Why? Because if there is a bad connection one filament can find a ground path via
the other filament, as long as its off. You'll notice this bulb is dimmer since it is running both filaments in series. The usual problem is in the shared connection that is the base of the lamp, make sure that the wiring to the socket is in good shape.

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Roger