Headlight not working

[BigDick]

I've had the problem for quite a while, the problem was "fixed" by someone else. They spliced from a keyed brown wire (it had power to it only when the key was on) to the green wire coming from the headlight. This bypassed the whole rest of the harness, I could remove the headlight fuse and the light would still work. I removed the reserve lighting unit today along with the wire splice. No headlight. That green wire goes from the headlight straight to the left switch, the black is the ground, and the yellow wire goes to the warning light, the reserve lighting unit, and the left side switch. What do I check from here? I would think that if I had a weak connection the light would flicker or be dim, but anyway tomorrow I'm going to follow the harness and check all my connections.

[DiverRay]

Do a search on "headlight not working". There is a diode, a one way electrical valve so to speak, buried in the wire harness. If the diode has fried, and they do sometimes, you don't get any power to the headlight relay, and no headlight.

[BigDick]

Thanks Ray! found it by searching "headlight" "diode" Here's the thread if anyone else has similar problems. Now if it is the diode that's bad, do i need to replace it or just run a jumper wire from connector to connector?

[BigDick]

here's where I found the headlight diode. Just above the valve cover. I did have to jiggle the harness to the rear just a bit so it may actually be just a git forward or the valve cover.

Here's both pieces of my diode. Do I now need to go to the Yamarobbers and get a new one through them or just jump the wires across and pretend there never was a diode there?

[Ivan]

diodes are diodes. Chances are you can find one at radio shack the same size and splice it in. Just be sure its in the right direction.

[BigDick]

If I do hook it up backwards will it hurt anything?

[Ivan]

not sure, I don't have the circuit memorized. Usually diodes have a stripe printed on one end that signifies the positive side (IIRC). I cant tell from your picture if it has a band on it, the plastic sheath obscures it. If you see a stripe on one endsolder the new one in the same way with heatshrink over the whole thing, and it should work.

John would be the ultimate answer on this one, hopefully he will chime in. He will more than likely know which is positive.

[BigDick]

Here's the diagram, you can see the diode just below center. Does the image designate the direction of current I wonder. . .

[Ivan]

Yes, typically the arrow indicates the direction of bias (current flow). IIRC the stripe coincides with the point of the arrow. Its been a while since I have read electrical diagrams, so I am a tad rusty.

[MrOzz]

Most of the time a wire diagram will show the proper direction of current. I would say yes that the diode is shown in the proper direction.


(Looks like Ivan replied while I was typing lol)

[BigDick]

Thanks guys, I'll check at radio crack tomorrow and see what they have for replacements.

[greatnw]

Hey BD,
I just did the diode replacement and whatever I did, did not work. I got the only 12v diode my local Radio Shack had. Did a nice job IMHO of crimping, sodering and shrink wrapping everything together and still no light so I simply bypassed the headlight relay. My original diode was actually busted with the wires disconnected. I asked my electronics buddies about mine having a single blue stripe with a white body and the one I got had a red body with a black stripe. They said to get the right one and try again! I'm fine with the way it is working now, so until I get the exact replacement I'm running with the relay bypassed.
Good luck.

[XJOK2PLAY]

Hey BigDick...

The only thing I might add to what Ivan has already said, addressing you're question "Do I need one?" A diode is just like John said, it's like a "check valve". It lets current only flow in one direction, so it can't backfeed into the rest of the circuit, which could energize something else that would normally be controlled by a switch... in other words... switch could be off on another circuit, get power from the backfeed w/o the diode, and cause it to work.
Pretty common on circuits w/ light bulbs (filiments).

So, yes... I'd definitely replace it.

Aside from direction of installation... ampacity (wattage) would be what I'd watch about. (How much power draw the diode is rated for.)

Clear as mud now? LOL

[BigDick]

I understand what everyone's saying, now I just gotta figure out if I can get one for less than it's equal weight in platinum thanks all for the explanations.

[thebottle]

Found this thread because I have the same problem. My headlight is not working. The previous owner had "fixed" it by splicing the brown wire for the brake switch into the headlight socket, . I wired the headlight socket back the way it should be and then found the actual problem which is the diode.

Took awhile to find it, but found it here. And this is what it looks like, not much left to it. It has literally burned out and turned into powder, .

Now I'm posting here because I have a question. I'm not familiar with this and couldn't find any specifics through searching, but will pretty much any 12v diode work? But what amp or wattage should it be rated for?

I was looking at this one, although I don't need 20 so I think I will see what the auto parts stores have in stock if I can just buy a single one.

By the way, I started it up for the first time after meticulously cleaning and then bench syncing the carbs... and it runs amazing. Still need to sync them, but damn if it doesn't run great already. Before I had all kinds of issues, mainly idle hang. Not anymore.