Thanks.
The only thing I can think of is that you have a dead short in the solenoid.
The way a solenoid works is that you have a big cable in from the battery, and another big cable out to the starter. There is a electro-magnetic plate inside that is activated by the key (one of those two little post on the front of the solenoid, The "plate" contact both of the big cable lugs and sends the battery power to the starter. The battery bolts in the solenoid are marked Batt and Start or just "B" and "S" - you have to have the "BS" straight (couldn't resist it).
I'm guessing you did have the big "B" and "S" cables hooked up correctly. And that you have the positive (+) cable to the solenoid and the ground (-) cable to the block (swaping those could cause what you described) Check that and then
FYI The solenoid has to be grounded to the inner fender to work - so does the voltage regulator - but neither should cause or effect what happened.
Try using a continuity test between the solenoid battery lug and the fender. If it lights, you have a shorted solenoid.
Good Luck