A fully charged twelve-volt battery can use to run three tests on the solenoid (magnetic switch). To check the pull-in coil, apply 12 volts between the 'S' terminal and the 'M' terminal on the solenoid. To do this, jumper wires are taken from the battery to the solenoid. The positive would go to the 'M' terminal and the negative would go to 'S' terminal. If magnetic switch is forced attracted, pull in switch is okay. The holding coil can be tested by grounding the 'M' terminal to the solenoid body with a lead. Then connect a jumper wire from the positive battery to the 'S' terminal. This should pull in the plunger. If the plunger continues attracted after the 'M' terminal lead is disconnected, then it is good. To check for return, push the plunger in by hand (operating it as you normally would) and place a jumper from the negative battery terminal to the 'M' terminal and a jumper from the positive battery terminal to the solenoid body and the plunger should not be attracted to the solenoid body.