That wire sounds like the oil pressure switch wire. To prove it, turn the key on, touch it to the block or the alternator case, and see if the oil light turns on. It plugs to the sender just under the exhaust manifold at the front of the passenger side of the block.
The silver pre-heater hose is broken on every one of these cars. It's in the way for the oil filter change and that's probably how it got broken.
It can be replaced or left like that with little consequence either way.
Make sure it can't get into the alternator "hot" terminal.
The rattles could be exhaust heat shields, which are common enough on these cars. They can be removed with a pry bar or a big scrwedriver easily enough. You won't miss them.
As for power loss, I'm suspecting 2 plug wires got switched. Verify the firing order and position on the dist cap. The #1 plug wire should be on the cap closest to the water neck/ thermostat housing. There is a tick mark on the dist body, under the cap, showing where #1 should be. The dist rotates clockwise when viewed from above. (How else would you view it?)
Good luck!
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Rob Bareiss, New London CT ::: '87 244DL/M47- 229K, 88 744GLE- 218K, 82 245T-181K Also responsible for the care and feeding of: 88 745GLE, 231K, 87 244DL, 239K, 88 245DL, 246K