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Old May 16th, 2021, 04:06 PM   #6
InvisiBill
EX500 full of EX250 parts
 
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Name: Bill
Location: Grand Rapids-ish, MI
Join Date: Jul 2012

Motorcycle(s): '18 Ninja 400 • '09 Ninja 500R (selling) • '98 VFR800 (project) • '85 Vulcan VN700 (sold)

Posts: A lot.
Blog Entries: 1
MOTM - Aug '15
The headlight circuit isn't too complicated, though it does have a few things to trip you up.

The relay keeps the headlight turned off when you first turn the key on. One of the yellow wires from the R/R forks off and goes through Diode B to the headlight relay's coil. When you start the engine and the R/R starts generating power, it flips the relay. The output of the headlight relay also forks and goes through Diode B into the coil as well, so that as long as you keep headlight power going through the relay, it keeps it latched. You have to kill the power (i.e. turn off the key) to turn off the relay.

Power is fed from the fusebox on the gray wire into the relay. It goes out on the blue/yellow into the left control (and forks off to the diode/relay as previously mentioned). It also forks off to the low beam, which is always on (after the relay latches). The lo/hi switch in the left control actually just turns power off/on to the high beam, going out on the red/black wire to the high beam and dash indicator.

If there's no obvious short, it could be your R/R. At idle, it would be putting out less than at higher RPMs, so it might be fine as long as it's just sitting there idling. However, as soon as you get it up to speed, it might be putting out too much voltage and killing the relay.
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