So what is running on the "back up" fuse. Its a 7.5a fuse. The S is a AP1 and i can take out the fuse and the car runs good. What is the fuse used for? Im trying to figure out why the car will not start after sitting for more than 3 hours. I have gotten several new batteries,and it does not help the problem. I know that the car when running draws 14.1 volts and then as soon as i turn off the car its starts dropping rapidly (with the key out of the ignition).