No power to headlight.

[Smittyboy]

I recently went on a nearly 2 hour ride at highway speeds. When I returned I noticed when it got dark I had no headlight. I checked the fuse and it was popped. Thought all is well, replaced the fuse, and still no headlight. Now, the fuse remains unpopped, but no light. There was some corrosion on the plug and prongs of light so I scrubbed them clean. No light. Tried several bulbs I had lying around (filaments all looked good and one led) and no light. IDK where to begin. Electrical issues are voodoo.

 

[Gary in NJ]

Do both the low beam and high beam have no power while the ENGINE is RUNNING? Could be as simple as burned out bulbs. If the bulbs are ok, then it’s time to get yourself a multimeter and start checking the voltage path to see where it ends. Once you know where the voltage ends, you can check for continuity to see where there is a short or open circuit.

 

[Ohendo]

What Gary said. I emphasize his bit about "ENGINE is RUNNING". Just turning the bike key to 'ON' will not send power to the headlights. You have to start it first; you can then kill it with the red switch and it will stay on (power will be present, at least) for troubleshooting. (You probably know this, having had your bike for so long. Just had to throw it out there.)

 

[bigborer]

It's also possible to enter the diag mode, and start the headlight relay from there (engine off)

 

[Smittyboy]

I know the first question of tech support is "Is the computer plugged in?" but I've had the bike since new in 08. I'm aware the engine needs to have run before the lights get power. I tried several bulbs including an led so all being burned out is very unlikely. I'll swing out and get a cheapie meter and try to start following wires. YAY!

 

[trepetti]

I know the first question of tech support is "Is the computer plugged in?" but I've had the bike since new in 08. I'm aware the engine needs to have run before the lights get power. I tried several bulbs including an led so all being burned out is very unlikely. I'll swing out and get a cheapie meter and try to start following wires. YAY!

I know you know, but don't forget to put the bike into a mode there the headlights are on (bike running, running and shut off with kill switch, diag mode, whatever).

If it were me, I'd start by verifying voltage at both ends. Check at the fuse and at the bulb socket,

- If fuse ok and nothing at bulb, look for a 10 pin connector under the battery box. From there, Black/Green goes to the bulb, with solid Green coming from the relay. At the relay, there are 2 Red/Yellow wires that go back to the fuse.

- If no voltage at either leg of the fuse, it is either the fuse block or you are having other problems like no tail lights and no signals. That is HIGHLY UNLIKELY.

If you have a schematic it would be helpful, but above are the basics.

FYI, not sure how experienced in using a meter, but when tracing voltage it is important that you use a reliable ground. Find a chassis bolt that is grounded or go right to the battery. If your ground is unreliable you will end up with irrelevant test results and waste a lot of time chasing your tail.

 

[Motogiro]

Some additional info that may help. There is a relay that is powered once the key is on and then activated by the ECU once the engine is started. That relay is fed by the fuse that becomes live when the key is on. The ECU provides the ground path for the relay coil. So that relay could potentially be a source of the problem. It is located under one of the pods (left or right).
there are 4 wires attached. 2 wires are red with a yellow tracer, 1 yellow with a black tracer and 1 green.
When the key is on, the red with yellow tracer wires should show +12 vdc
When the engine is started the relay should be activated and you should see +12 vdc. on the green wire.

It is important to also check that the black wire on the headlamp plug hasn't lost it's ground path.

Even though a multimeter is most import for different types of tests and trouble shooting, I mostly use a 12 volt test lamp to quickly assess go/no go testing.

 

[Smittyboy]

I'm hoping the continuity beep on the tester will work. Unfortunately, I've been slammed and haven't seen the bike. Getting back at it after work tomorrow. Thank you to all who have chimed in. Hoping I can just replace a relay. I changed the popped fuse, so I hope it went before some really gnarly stuff went with it. Hoping the relay crapped out and popped the fuse. We'll see how it goes tomorrow.

 

[Smittyboy]

Not only was relay okay, the fuse did it's job PERFECTLY and a connector pulled apart. Put the male in the female (giggity) and presto chango bob's your uncle. All is well.

 

[agf]

its probably something you have checked but maybe not....

I found that with the slight strain of the wiring on the headlight I had rubbed through the insulation and had an intermittent short( never blew a fuse but headlight would go out when the bars were turned, but not always) - took me ages to find what I thought was the problem, re-insulated and then a couple of months later same thing started to happen, at least I knew roughly where the issue was. But this time it was the plug( H4?) that the lamp sits in, it had melted due to the shorting out. Replaced the melted plug with 3 spade crimps during last years lock downs to get me out of a bind and that fixed the issue. Then once we had freedom again put in a new plug soldered all the joints and it was peachy.

Edit: I posted this after I read Clif's response then didn't see Smittyboy had responded (twice). that electrical stuff can be mighty tricky!

 

[bigborer]

Do you remember where the intermittent short was at?