I've got a 1973 Comet with a 200 strait six. The car won't crank. When you turn the key all you get is one click and then power for the whole car shuts off. Lights barely visible and horn won't honk. You can disconnect the battery and hook it back up and then the dash lights will light up and horn will work until you turn the key then you get one click and everything shuts down again. I have already replaced the voltage regulator and starter solenoid. I tried jumping the solenoid and got no results. Battery reads 12.4 volts. After I put the new voltage regulator on when you turned the key I would get a bunch of rapid clicking sounds and power would stay on afterwards. It went back to its previous state of one click and then nothing after I tried jumping the solenoid one time.