Kawasaki Versys Forum - View Single Post - How do I test the headlight relay?
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post #19 of (permalink) Old 03-05-2016, 11:32 PM
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Post 9 / Starter Solenoid discharge diode

Originally Posted by Beezerboy View Post
sooooooooo.... looking at the diagram, the headlight relay is always in series with 2 diodes and the starter relay coil. that would indicate that the light relay is a special monkey right? the lighting relay must operate at a lower voltage and yet current limit enough to keep the starter relay from coming on uncommanded, so I'm guessing it's not an off the shelf relay & think that is an important point. a test as described is ok, but prolly not a good idea to go full voltage too long.

1wizard.... ever test one on a variable power supply to see where it comes in? just curious. I see what they are doin.... any time you push start, it puts plus on both sides of the headlight coil & turns it off.

the Concours had weirder one than that... it used the starter's armature as a generator to engage the rely as it winds down after start, then the relay would latch with alternator power
In actual fact any 12 volt relay would work, diodes provide blocking only, one diode is for latching the relay, and one for pulling in / rectification from the stator.

The ground or negative side of the headlight relay goes to the positive
side of the starter solenoid , keep in mind there is a starter relay mounted beside the headlight relay , and starter solenoid located at the main fuse. So having positive on both sides of the coil produces 0 current flow. the starter solenoid coil is a heavy gauge low impedance coil, if this coil stayed on for 5 minutes it would burn out. If I was really curious I would measure the resistance of the starter solenoid coil wire, and one day I may do just that. It may be that Kawasaki specs the relay for 10 volts, I don't know, one thing that could be done is measure the VDC across the starter solenoid coil with the bike running, that is the voltage drop across the solenoid, say it was 2 volts at 14.2 VDC output.

So, once the bike starts and alternator puts out 12 VDC, the positive energy/ current, goes into the headlight coil, through the coil out to the positive side of the starter solenoid, through the starter solenoid coil and out the solenoid coil to frame ground.

You want to prove this, start your bike, disconnect the starter solenoid positive or negative wire once it is running, your headlight will drop out.
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