Dead Headlight

[barrelguy]

Just getting the old girl ready for the season and find that the headlight doesn't work. Fuses are good, installed new bulb, checked/cleaned all connections, all other lights work as they should, just no headlight, ALso checked all the continuity I could think of - seems good. Anybody have any ideas? Many thanks.

[crazy steve]

Things to check: diode going to the headlight relay, the relay, left handlebar control connections, high-low switch, headlight ground.

Try bypassing the headlight relay first (it's under the tank, above/forward of the coils). Unplug the relay, check for power on the red/yellow wire, if present then jumper the red/yellow and blue/black wires together. If the light now works, then either the relay is bad or the diode has failed. The diode will be located in the white wire coming to the relay from the alternator; trace it back until you find it (it will covered with a bit of vinyl) and check that.

It's usually one or the other of these. If not, you'll need to check for continuity from the relay through the handlebar controls and on to the light.

[barrelguy]

Thank you Steve. I'll continue the diagnosis.

[Eastcoaster]

Mine was the headlight relay under the gas tank bad connection on the plug

[barrelguy]

Ok So I have power on the red/yellow, jumpered the red/yellow and blue/black and voila! headlight works. So it will be the relay or the diode. Just for fun I checked continuity on the relay and it is there on the R/Y and B/BL posts but not on the other side. What exactly does a diode look like??

[hamjam]

try starting the bike

[CaptonZap]

try starting the bike

and checking voltage at the white wire at the relay. Set the meter on AC, and you should get 5-6 volts. (The diode makes it a pulsating DC voltage, which confuses the DC meter.) If you have it, the Reserve lighting Unit is the probable culprit. Just went through this routine.

Andreas has a good price on RLU's.

CZ

[barrelguy]

All is good. It is very handy having Andreas living just down the road! Also scored a replacement speedometer for the one that died last year. Thanks for the help.