1985 gmc sierra won't start, won't turn over

1.wear safety glasses .check fuses for bad fuses. disconnect battery positive before you work on cleaning connections after cleaning is done the last thing is reconnect positive cable the last thing. When you turn the key do you have dash lights ? If no, clean battery connections and cables even if they look good + and - even cable to block connection. If yes. Continue to 2. 2.When you try and start it does it go click click click? If it just clicks check connections again make shure clean and tight. Disconnect positive before you work on connections always. 3. Or does it turn over and start to try to start but just not start? Back fire pop sound ? Check fuses and fuel pump , there are a number of things it could be from starter relay to temp sensor wire . That's the basic stuff you can check your self.good l uck , invest in a shop service manual not a chilton or climber but an official service manual it's well worth the investment .

your ignition switch the electrical part could be bad.