Start at the alternator and LOOK at each connection back to the battery.
Take them apart if you must. Then check the frame, body and engine grounds
the same way.  It sounds like you are taking power away from the fuel pump
or computer with those loads.  Then you get to follow the hot wire back from
the battery or junction to the main fuse bank.  It is a tedious process, I
know. That is why a former employer put up with my crap.  Look for damage
insulation, or any wire that looks or feels odd.  A quick overview before
you start the detail work may help. Do the Grounds first, they are shorter
and easier to deal with.  just loosen and clean and reconnect.  You'll find
it eventually.