A) Create conditions under which voltage is present at the point of the circuit to be checked.
Example:
A - the ignition is on.
B - ignition and switch No. 1 (SW1) included.
C - ignition, switch No. 1 and relay are on, switch No. 2 is off.
b) Connect negative (-) voltmeter lead to «earth» or negative battery terminal, positive (+) output - to the point being checked (connector pin or outlet of the electrical appliance). The check can also be performed using a test lamp.