Happ is not in the business to help us build our one off cabinets. They are there to provide the parts necessary for the people who work on amusement games for a living.
Of course they don't provide instructions. If you know enough to order the parts, they assume you know enough to install it. It's like that for any place that supplies to the professional. If you buy a receptacle from Home Depot, chances are good it will have wiring instructions in the package. But go down to your local electrical supply house, all you'll get is a receptacle and bill. If you are lucky, they guy behind the counter might know something about electricity, but chances are good he just knows how to pull the stuff off the shelf.
The parts providers like Divemaster, Ponyboy, GGG (Randy), Bob Roberts and the others are very helpful when you get into a spot. As is everyone else on the forum.
As CheffoJeffo said, reasearch goes a LONG way. I can't remember a topic (not that there aren't any) posted about controls available from Happ where it wasn't mentioned that purchases should go through a 3rd party.
You can also expect some people on this forum to get annoyed when they see the same topic pop up again. Jeffo, for example, has been on here since Christ was a child, and I'm sure he's seen this more than he'd care to count. Not that he's annoyed, but you see the point. Just ignore the people who get ugly about it, and thank the people who help.
Search the forums and ask questions. NEVER just jump in with both feet; all you'll do is get in over your head.