Same thing, just done by the mfg. instead of an add-on. As per Resto. Testing is easy, the wire that feeds your starter solenoid comes off the cube relay, so, if it is getting 12V when you hit the start switch the relay is good. Unplug the wire off the solenoid terminal when testing. Go to the Scag site http://www.scag.com/manuals.html and locate your model. Then download the owners manual, it should have a wiring diagram to check out. JimQ is right on with the solenoid descriptions.