One side of the load/extruder, is tied to V+, e.g. 12V. As a result V+ appears at that point always, as long as psu is turned on.
The mosfet is a low side switch, meaning mosfetsinterrupts the gnd/low side of the load. For example, when fet is off, the load would start working if it could find an alternate path to gnd.
If you want to check if its working properly, measure the voltage between the 2 leads of resistor, to each other. When fet is off, both of them will be at 12v, and their difference =0v between. When fet is on, one side is pulled low, so all supply voltage appears across resistor, giving difference between resistor leads =12v.
The mosfet is a low side switch, meaning mosfetsinterrupts the gnd/low side of the load. For example, when fet is off, the load would start working if it could find an alternate path to gnd.
If you want to check if its working properly, measure the voltage between the 2 leads of resistor, to each other. When fet is off, both of them will be at 12v, and their difference =0v between. When fet is on, one side is pulled low, so all supply voltage appears across resistor, giving difference between resistor leads =12v.