Sounds like we are all assisting in solving what over the years has been a frequent problem for all of us. What I would like to add to the discussion is a few observations from assisting others with repairs. Probably the most common and misunderstood part of the wiring is how important correct grounding is. First let me say that the ground wires used should be as heavy as possible, typically 18 gauge is good. DC which is what we are using goes through the entire cross section of the wire, unlike AC. Second, caution and care should be used to avoid creating what are called "ground loops". If you were to take a metal box and from corner to corner you place a wire and connect it to the box you have now created a ground loop. That is the negative or ground now has two electrical paths. Most people will take a ground wire to one point, attach it to another point or circuit, then to the next point and so on. Now this one ground wire must carry the current from all the circuits and if the ground wire is small you are basically overloading it so grounds are recommended to be heavier than power. Using relays can cause problems if you forget to add a diode across the relays coil. When you energize a relay it becomes an electromagnet. When you remove power from the relay the electromagnetic field colapes and puts voltage back into the power line. Just something to keep in mind. Using the twisting technique for all your signals and power feed. Simply take the wires, put them in the end of a drill and twist them together! You will probably enjoy this more as it will seem as if you are routing only one wire and not several and your installation will probably look much neater. The advantage of twisting is that the wires now act as small capacitors which will reduce unwanted signals from ajacent wires getting into you circuits. The uses of 4 different value capacitors helps in most situations. Start with a .01 mfd, in parallel with a .1 mfd, in parallel with a 1 mfd (preferably a tantilum), then add a 10 mfd. Each value will act as a "short" to certain frequencies depending upon its value. Again I hope this is of value to anyone reading it.
Just one more wire!