Securely mount the 89D standoff bracket to a wall or plywood using two screws.
Route the cables over the standoff bracket from either the top or bottom, and then out through the sides, depending on which side they will terminate. When using a 25-pair
connecting block, all pairs will terminate on the left side.
When using a 50-pair block, 25 pairs will terminate on the left, and 25 will terminate on the right side.
 Carefully snap the 66 block into place on the standoff bracket. Separate the pairs, routing pairs 1-12 through the upper bracket opening, and pairs 13-25
through the lower bracket opening.
 Strip approximately three to four inches of sheathing from the cable, leaving the twists in each pair up to the point of termination.
FOR DATA: The first pair will route through the first slot in the side of the block. Split the pair, sliding one wire up and the other wire down to the metal termination clips. Pull the wire through the slot with your hand, then use a punchdown tool to attach the wire and cut off the excess. Skip a slot in the side of of the block, then route the next pair through the next slot, and
repeat the termination process.
FOR PHONE: You can use the same procedure shown for data, but many people
prefer to split the pairs before running the wires into the slots on the
side of the block. It's faster, easier, and works just fine. Wires will be in
each slot - DON'T skip alternate slots.
 If you are using a 25-pair block, remember that all four of the silver
clips are connected. When a wire is punched down on one of them, the remaining
three are live and ready for connecting.
 If you are using a 50-pair block, think of each row of four as split
right down the middle; two connections on the left and two on the right. You may
terminate the cross connect on the far right side. To make a cross connect live,
use a bridging clip on the middle two clips. This connects the two sides and
gives the cross-connect itís signal. This type of connection provides convenient
quick disconnects for making a jack live or dead, and is helpful for diagnosing
IMPORTANT NOTES: Wires always enter from the top of a clip, and get chopped-off at the bottom. Don't put more than one wire in a clip. Make sure your punchdown tool is perpendicular to the block -- not tilted upward as in the photo. It's sometimes better to tilt it slightly downward.
(Based on info from Leviton, who also supplied the photos)