little unclear as to what exactly your talking about, on the starter motor there are 2 wires
1 - big fat positive straight from the battery
2 - a normal sized wire that comes from your ignition barell, which is your solenoid trigger wire
if that solenoid trigger is earthed it will just cause a dead short = bad, might explain your uber voltage drop.
if it was the trigger wire that was earthed, I would expect no cranking at all
exactly how is it earthed?