I haven’t done the 3 headlight mod, not because I’m scared or lazy, but I don’t really ride at night and what few times I did the low beam headlights seemed enough for me, this is because the high beam is pointless as it never seems to give you the light where you need it. So I can see why the 3 headlight mod is a popular one.

I did some reading on the mod and it seems there are a misconception about using a relay as opposed to wiring up a Diode. Some say when using a diode it will overheat and stop working. This can be true if you face the diode the wrong way in the circuit….I’ll explain

I traced the circuit down in the service manual and the low beams are relay driven and the high beam is powered directly from the switch itself. Page 443 has the full wire schematic
Service manual

Here is the break down

Switch on handle bar
Low beam – Pin F – Dark Green
High Beam – Pin E – Yellow

Relay in fuse box
Coil High – Pin 25 – (relay trigger input)
Relay out – Pin 29 – (relay high current output)

So the low beam wire doesn’t have a real load on it because it feeds the relay as a trigger, the relay output is where the load of the headlights are on. (Switch pin F —>relay trigger, Relay output pin 29—->factory splice—->headlights)

The high beam wire coming from the switch actually is connected bulb directly so it has a load on it. (high beam wire Pin E—–>high beam headlight)

So if you want to use a diode, make sure you put the Cathode end(silver stripe) towards the Dark Green wire(low beam) and the Anode end on the Yellow wire. This will have the low beams operate normally and the high beams use all 3 lights. Keeping an relay energized take very little power you could use a 1-3 amp diode.

Now it is possible, if someone were to flip the cathode end to the yellow side, you could actually cause a failure in the diode. if the diode amp rating is lower the the circuits amp draw it would overheat and fail. You would probably need a 10-15 amp diode to handle the load. You would know if you hooked it up backwards, if you turn on the low beams and the high beam turns on too and if you turn on the high beams and the low beams turned off.

There is nothing wrong with using a relay but you don’t have to use one if you don’t want to. A relay just requires a couple more steps(connections) as opposed to the diode.

Hope this clears up any Confusion. I posted this in the 570 section as I only have the 570 service manual but I am sure most other models are the same.