Sound like it could be a short under the playfield.
I'd be checking around the coin switches and those loose wires again.
The loose wires may not be re-connected correctly to "daisy chain" to the next switch.
Run full switch diagnosis to see exactly what is and isn't working.
The switches for the pop bumpers and slings are part of the special solenoid switches and not part of the switch matrix.
Have you seen the repair guides here? (EDIT Link Removed)
And do you have a Manual?
http://www.ipdb.org/files/310/Williams_1980_Black_Knight_Operators_Handbook.pdf
