Replacement keyboard will not light up?

I Just bought a replacement keyboard, and top case, after installing everything worked fine except that the backlite on the keyboard would not work, when i would turn up the brightness the blocks on the screen would fill up but nothing would happen. So it was taken apart to see if something wasnt connected right, put it back together and then proceeded to try it again and i got a cirle with the line through it. So maybe there is a connection not fully connected somewhere? Should i try unplugging and replugging the connections? i also tried resetting the pram , etc but still nothing happened after that. ( that was before i took it apart again)