electrical problems

ok, my 91 blazer does not have turn signals whn the light switch is on aswell the brake lights stay on,when the light switch is off every thing works fine.when the truck is off & the brake pedal is depressed the instrument cluster & radio illuminate.any suggestions would be greatly appreciated

do you have trailer wiring installed?? if the park light wire and turn signal wires are touching power is fed through the circuit backwards and do whats happening to you. also if the wrong type of bulb is installed it can do this. check the wires at the light sockets if there is corrosion power can get fed back too. another likely suspect is the light switch they get corroded and do the same thing. so check all the wires, sockets, switch shouldn't be too hard to find the problem. good luck!!

thank you very much. it was the trailer harness.....i thought it was some thing more complicated.