taillight problem on s10

my s10 has taillight problem, works great during day but after dark lose one taillight and when you step on brake same taillight the reverse light lights up

It's likely that a ground connection at the lamp socket or vehicle harness for the lamp has corroded or lost connection. This causes the brake lamp filament to attempt to ground through the higher resistance running lamp filament and lighting circuit.

Thanks for the reply I was thinking that it might be in the daytime running light switch by the front speaker on the dash, but I'll have a good look at the grounds for the harness and around the tail lights as well I'll let you know how it goes. thank's