Quoted from markmon:These aren't too hard to troubleshoot. The spike shakers have only two wires. It's a 12vdc shaker so you can give it a bit of 12vdc on those two wires and see if the shaker moves. If so, problem is upstream if not problem is shaker.
I'm surprised the shaker would only be +12v. The manual (WWE, KISS) doesn't tell what voltage that connection is, but I expected more than +12v.