To minimize electrical resistance, the battery and starter motor are connected by using heavy gauge electrical cables. From the battery, there is a major power supply wire that goes directly to the starter while smaller gauge wires take care of other electric system needs. The starter engine is a DC type electric machine with its specifically designed construction that leads to great output due to intermittent working and at high speed rate of rotation. Solenoid engaged by the ignition switch pushes forward the starter handle on one end while connecting it to the battery at the other end. At time when "START" is turned on ignition, solenoid plunger moves this gear such that if teeth fit properly; then cranking takes place in an engine. To prevent excessive spinning rate, one-way clutch allows pinion spin faster than starter shaft when starting an engine. So, once you release (key) switch for ignition, this solenoid will be de-energized hence disengaging starter. There are some starters which use separate relay as current controlling device but not all.Starter motor failure can be detected by either no action after key turning or else clicking sound.Including circuit testing, solenoid and cable tests are done for troubleshooting.Starting system removal and installation procedures may vary depending on what kind of engine your vehicle has but generally consist of disconnecting the battery, removing the starter, inspecting it then reinstalling it.Therefore due to wear consistency replacing both solenoids or relays with new starters is recommended.