To set up your jackpot, try this - it worked for me:
First check your jp is in the closed position; now disengage the the pecker blade from the index wheel; rotate the index wheel to the 12 win position and insert the pecker blade. If the pecker blade is now half way down the slot, look at the clock face. You should have the large hand at 12 o clock. Disengage the pecker blade and rotate the index wheel so that both hands are on 12 o clock.
Now check the position of the pecker. It should be all the way in the slot. This is the jackpot position.
Lift the coin tube to the max. This should trip the jp. So at this point if your jp did not trip, check the distance from the trip rod to the inside bottom of the metal 0 shape loop. If there is a gap, you need to bend the trip rod. Do this by holding the rod inside the loop with pliers and bend the front of the rod down with a second pair of pliers. Doing it this way will prevent distortion at the other end.
Now disengage the pecker blade and turn the index wheel just to take it off the jp position; lower the coin tube, and bend the rod just slightly more.
Back to jp position, lift up the coin tube and see if this has worked. If not, just keep bending the rod until it does.
Mystery "L" bracket:
My idea on this is that on a jp win 12 pennies are paid from the coin tube, but none from the jp, because if the "L" bracket is positioned over the trip rod it can't trip the jp. So the punter calls the bag man complaining. The bag man then pays the punter the other 12 pennies from his bag of coins, saving him time fiddling around inside the mech resetting and refilling the jp.
But of course this is just a guess.
Hope it makes sense.