Stalls with electrical loads

Engine ground looks good. 12V to 11.5V at battery in gear not good, should be 13.8V to 14.5V if cold temperature. 5.4V at coil is low by a couple volts, assuming your measurement is on coil + ? Low voltage at battery in gear could be, low idle speed, loose belt, poor connections ..... a good battery will be closer to 12.5V, even without alternator, if it has a good charge. The positve battery terminal looks oxidized in picture. Have you cleaned them?

Never pull plug wires on electronic ignition, to check, use spark tester or short to ground.