Checking the relays
Check each switch for continuity with the pocket tester. If the continuity reading is incorrect, replace the relay. 
1. Disconnect the relay from the wire harness.
2. Connect the pocket tester ( × 1) and battery (12 V) to the relay terminal as shown.
Check the relay operation.
Out of specification → Replace.
Starter relay

1. Positive battery terminal
2. Negative battery terminal
3. Positive tester probe
4. Negative tester probe
Starting circuit cut-off relay

1. Positive battery terminal
2. Negative battery terminal
3. Positive tester probe
4. Negative tester probe 
Headlight relay

1. Positive battery terminal
2. Negative battery terminal
3. Positive tester probe
4. Negative tester probe 
Radiator fan motor relay

1. Positive battery terminal
2. Negative battery terminal
3. Positive tester probe
4. Negative tester probe
Test yourself
A quick Yamaha YZF-R125 quiz: every answer comes with an explanation and a link to the manual page.