Viper car alarm lock and unlock works fine but will not let key turn

SOURCE: Viper auto alarm

Check the wiring again, The Ford company uses a light control module in their vehicles. It is fact that the main CPU (Central Processing Unit) stays on line for about 45-60 minutes after the vehicle is shut off that this could show enough of a voltage drop to trigger the alarm when it goes off. If at all possible you may want to monitor the voltage after shutting the truck off and see if the alarm triggers at the same time the voltage drop decreases across the battery after the CPU goes to sleep (45-60 minutes). I hope this helps or at least explains why you may see a foltage draw while testing. Remember to be patient while waiting for the computer to shut down. it will.

Good Luck,

SOURCE: Viper remote starter sets off alarm.

Whoever hooked up your system did not hook up the factory alarm disarm and arm wires. Your car thinks it is being stolen as a result of this. You need to get a wire diagram of your car and hook up the proper wires.