You should order a schematic from Pinball Resource. IPDB does not have one sadly.

If it is not resetting at all, and it sounds like it is not, then I would suspect the reset coil. Are the wires securely soldered to the coil tabs? Is the really thin wire that makes up the coil also attached to those tabs? Also, check all your Jones plugs and make sure no wires have broken loose. If you haven't already, disconnect each plug and clean the pins with a wire brush.

You could also try attaching a jumper wire with a couple alligator clips from the power lead of another playfield coil, say a slingshot, to the power lead tab of the bonus unit step down coil. When you activate the slingshot, the bonus unit should step down, If it does not, I'd suspect a bad coil.

If you have a multimeter, you could disconnect one lead from the step down coil and measure its resistance. If it's open, the coil is bad. It's probably not shorted or you'd be blowing a fuse.

Finally, is the outhole switch closing when a ball is in the hole? Don't use a finger to check; use the ball.