A) Disconnect the negative battery terminal or power supply wire so that the test points are not energized.
b) Connect an ohmmeter to the circuit points to be tested.
If there are diodes in the circuit, check when changing the polarity of connecting the ohmmeter. When to positive (+) side of the diode connected negative (-) the output of the ohmmeter, and to its negative (-) side - positive (+) - there must be conductivity of the circuit. When changing the polarity, there should be no conduction.
V) When testing circuits, use devices with high input impedance (not less than 10 kOhm/V).