Testing a starter relay is quite easy.
basic equipment needed is 12v battery with 2 x wire i use crocodile clips .
you can also use a small test bulb as well .
if you need to buy a new relay then try here on Ebay UK
or you can invest in good and safer tool like the 12v powerprobe and
snap of test light probe I bought and are excellent .
I always have a fully charged 12cv battery with crocodiles knocking
about it saves loads of hassle
The relay , the small terminals are what connect to your starter
button and carry a lot less current .the larger terminals
are connected direct from battery to the starter
motor so need larger wires to carry the
massive starting currents .
I am using the power probe here as its safer but you can just as
easily connect the 12v negative to one side and tap
the positive on the other side you should hear a
click as you touch the positive and remove it .
You can go a step further and add a test light to it and confirm
current it going through the secondary circuit .
to test with a lamp you need to connect one end on test light circuit
to battery positive and the to one of the relays larger terminals
and then use another cable from second larger terminal to negative of
battery ill do basic circuit diagrams at bottom of page .
Now when you put power to the smaller terminals it should click but
also the light should flash on and off as you tap power .
OK not the best , never have been very good with Windows Paint
⚠️ Safety Warning: When testing relays with a battery, avoid shorting the terminals together. Large currents can cause sparks or burns. Ensure you are working in a well-ventilated area away from fuel vapors.
How to Test Yamaha YZF-R125 Motorcycle Relays
A relay is essentially an electrically operated switch. In the YZF-R125, the starter relay (solenoid) allows a small current from your handlebar button to trigger a massive current from the battery to the starter motor.
1. Equipment Needed
12V Battery: A fully charged motorcycle battery.
Jumper Wires: Preferably with crocodile clips for secure connections.
Test Light or Multimeter: To confirm current is passing through the high-load side.
Optional: A Power Probe or a specialized relay tester for safer, faster diagnosis.
2. Identifying the Terminals
Most starter relays have two sets of connectors:
Small Terminals (Primary Circuit): These connect to the starter button circuit. They require very little power to activate the internal electromagnet.
Large Terminals (Secondary Circuit): These are the heavy-duty posts connected directly to the battery and the starter motor. They handle the high amperage required to crank the engine.
3. The "Click" Test (Primary Circuit)
This test determines if the relay's internal coil is functioning.
Connect a jumper wire from the Battery Negative (-) to one of the small terminals.
Momentarily touch a wire from the Battery Positive (+) to the other small terminal.
Results: You should hear a sharp, distinct "click" every time you touch the terminal. This indicates the internal magnet is moving the switch contact. If there is no click, the relay is likely dead.
4. The "Continuity" Test (Secondary Circuit)
A relay can "click" but still be faulty if the internal high-power contacts are burnt or corroded.
Setup with a Test Light: 1. Connect one of the large terminals to the Battery Positive (+).
2. Connect the test light between the other large terminal and the Battery Negative (-).
The Test: Activate the small terminals (as done in Step 3).
Results: The test light should illuminate brightly as long as the small terminals have power. If the relay clicks but the light doesn't turn on (or is very dim), the internal contacts are failed, and the relay must be replaced.
5. Troubleshooting Tips
Corrosion: Check the large terminals for green or white crust. High resistance here will prevent the starter motor from getting enough power even if the relay is working perfectly.
Fuse Check: Many YZF-R125 starter relays have a main 15A or 20A fuse mounted directly on top. Ensure this hasn't blown before condemning the relay.
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