Tail Light troubles

I'm just bought a 2002 Sonoma 4x4 ext cab and i knew it had some problems, like needed a door handle, shocks and a basic tune up. But there is something fishy going on with the tail lights, they don't wory right at all. In the daytime all lights works pretty much fine besides back left signal light don't work, if i turn on the emrgency lights 2 front and 1 back comes on till i put my foot on the brake then they all go solid. Night time comes and the lights come on and neither back signal light will work and only 1 reverse light. Anyone tell me how many grounds are on the tail lights? and could this be a problem?? Any input on this would be greatly appriciated.