1987 Jaguar XJ6 When I turn the key to start the engine nothing happens

I have a 1987 Jaguar XJ6 series lll and was hoping you could help me with a problem I'm having? When I turn the key to start the engine nothing happens, the engine won't turn over. I tried cleaning the battery connections, I changed the ignition switch, checked the neutral safety switch, and it still won't turn over, the starter solenoid doesn't even click. The lights, radio, clock and all the buzzers work and the battery has 12 volts with the headlights on. If you can give me any help with this problem, it would be much appreciated.