We kept hearing and reading that there are other guachimonton ruins around the official site and I really, really wanted to see one of the sites. So when my niece was here we trooped out to the real Guachimontones and then went off in search of a ruin we'd read about. And we found it!
This a is little pyramid and there's a fence going along the side of it so you can't circle it, but it's clearly a guachimonton with the surrounding platforms. It's possible there's a ball court on the north side, but it's a really long ball court if it is. There's a stone wall going through whatever it is. There's also lots and lots of obsidian in the area.
Search for 20.741450, -103.882885 on Google Earth and you'll see the traditional circular mound in the middle surrounded with platforms. To get there, go past Teuchitlan and then turn right a few kilometers after town at a sign pointing toward La Pena just before a small hill (there is also the remnant of another old sign there and the coordinates are 20.689592, -103.917717). Drive down that road, go through the tiny pueblita of La Pena, and continue going mostly north until you get to a gate that may well be closed. But you can open it and drive on through. Take the next right (20.742571, -103.887319). The road was bad enough here than we walked up the hill, but when you get to top, go a little further and then you'll turn left at a path (20.740030, -103.884129) that goes right to the ruins.