I think the Cap Board, Houdini Pinball Coil Performance Improvement Kit (KIT0006-00), is one of the most important upgrades you can do to your Houdini. Mine feels like a new game after installation. Flippers are strong and decisive. PLUS my lower catapult works every time now, and it has been consistently missing for a year. I was THIS close to dremeling holes and bending, but I'm glad I didn't. This Cap Upgrade fixed it (my new coil setting for the lower catapult is 26).
https://store.american-pinball.com/collections/frontpage/products/kit0006-00
Make SURE you have the upgraded 48v power supply OR a Metal Box power supply installed before you order this board.
Just to recap what others have said in various posts and my own additions:
1. The included instructions are wrong. When you remove the first wiring harness, it's from J5 (not J2 as indicated) on the existing board.
2. See Jgaltr56's post (#11371) for a picture on where to install your new Cap Board.
3. I cut the wire ties to give a little more slack to the wire harness I pulled from J5.
4. Attach this wire harness to J1 on the new Capacitor Board (and make sure the Capacitor Board is oriented so J1 is on the left; it's backwards in the instructions). Make sure you attach this wire BEFORE you screw the Capacitor Board into the playfield so you make sure you have enough slack.
5. I bought an Irwin 6" Quick Change drill bit extender from Lowes to drill the pilot holes. This is almost necessary to avoid having to completely pull boards out. https://www.lowes.com/pd/IRWIN-1-4-in-Hex-Quick-Connect-6-in-Drill-Bit-Extension/1003019134
6. Hold the Cap board in place and carefully drill shallow pilot holes through the corner holes (make sure the plastic standoffs are on the bottom of the board, so the board "stands off" from the playfield. Some have reported these being on wrong as shipped by AP. Mine were correct).
7. Use the new wiring harness included in the kit to connect J2 on the new Cap Board to J5 on the existing board.