You need to introduce a new White/yellow wire that will go from the new rebound switch, daisy chain to the drop target white/yellow lug connection & then daisy chain it to an existing playfield switch that already has a white/yellow wire connected to it. (see the switch matrix diagram) For example left kicker switch has a white/yellow wire & can be connected there to the new rebound switch & drop target connection.

Same goes for other new wires, the new Green/Violet & White/gray wires required for the rebound switch/drop target bank, look at the switch matrix diagram & find an existing switch to tap into that already has these colours.

As you are adding new wires to the playfield, unless you have an old harness lying around with the exact colours you are looking for (like white/yellow wires ect) you may need to use different wire colours to substitute like just solid colour wires.

I have recently done a retro fit, I found to get them to work perfectly & to be very reliable I replace the wiper boards with new siegecraft boards & cleaned some good condition original contacts. I added some teflon lube to the boards (a tiny amount).

The key I found was to have an extra blank wiper (with no contacts) doubling up behind the other wiper with the contacts to increase tension. A single wiper doesn't seem to have quite enough tension to be reliable over time. I have come across few sets of used target banks that have 2 contact wipers per target, so I would say this is from the factory.

I adjust the distance from the back of the target to the very tip of the contacts between 8mm - 8.5mm on both contacts, this seems to be just right. Any more they are a bit too tight & don't drop properly & any less may not make a solid contact to the boards every time.

I didn't have a pic of the "cleaned" contact, but this illustrates what I mean with doubling up the contacts.

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