No crank/No Start. Battery fully charged, brand new alternator (they said my other was bad), starter tested and good. I hear only one click when I try to turn on but no crank, all lights, radio even A/C works with key in ignition. Also, cannot even turn on truck even with booster cables. Wires look good, terminals connected solid with no corrosion, fuses in interior look good. 326k miles... starter relay? How can I test? I have no mechanical skills unfortunately.