94 Gmc Yukon Brake Light Switch Not Working Right

[oneshot2stop]

I have a 1994 GMC 2dr Yukon and the brake light switch isnt doing its thing. I bought a new and it still doesnt light up the brake lights. I take it appart and trip the switch so to speak and it lights them up. But when I re-install it, it wont light up the brake lights. Is there supposed to be somthing between the back of it and the master cylinder to push it to activate it or what? There isnt a wiring problem, it just isnt getting enough pressure to get it to light them up. What I did was do a switchover, I turned a 92 into a 94 and all of the wiring. When it was in the original 94 it worked perfect. But, it seems to have hicuped since the transfer over. Could the master cyl. be a little longer coming into the firewall and engage the switch?