rear running light problem

[daluxsrt4]

My brother owns a 87. all of his lights work fine with the exception of his front turn signal goin out sometime. but now his running lights in the tails have gone out. they light up when he hits the brakes but other than that they are out. anyone have this happen before. (could it be they are shorting out due to the water that keeps gettin into his trunk compartment?)( were siliconin the tails tomorrow)