I have two dash cams with motion detection. need to install a constant power device with a battery saver (so if the battery gets down to 12.2 volts, will cut off power) plus a 3-outle cigar outlet. Can mechanic use the Body Computer Fuse center? Is there an open fuse to add / use in there? Also, adding a super loud Stebel Nautilus Compact airhorn with a plug-n-play wiring harness -- engine compartment fuse -- which one can I use?