Headlight problems

[HobbyMan]

For a while now out on the road, I have been noticing my headlight dimming down just the slightest bit on my 80G. A minute later it will come back up. As far as I know this only happens at high speeds, but I am not sure. Also, sometimes my headlight does not come on at all when I start up. I have checked the relay and it functions properly. I have replaced the fuses. The srange thing is that when I measured the lead to the solenoid from the alternator, I got a lower voltage than normal. The engine was running and It was reading around 9V. I believe there is a diode put in place between the alternator and the solenoed, but I can't find it. It shows it on the schematic, but i don't know where it is. I think that the dimming down of the light was because of an old fuse before I put new ones in. I am not sure about the headlight not cooming on. Does anyone know where the diode is actually located? It is in the middle of the last page of the 1980G suppliment on the 78-80 yamaha service manual. Other than the diode, what else could it be? Has anyone had a solenoid work sometimes and not work other times?

[TopCatGr58]

Hey HobbyMan,

It's most likely not your diode. The headlight relay latches as you said when it senses enough power from the ALT thru the diode to throw the relay. The dimming affect, not latching=turning on, etc., low voltage at solenoid, is a pretty good sign that either your battery is dying, or more likely your charging system is crapping out. And that is usually by the Reg/Rect getting fried.

There are testing techniques in the tech tips/as well as your manuals to help you rule whether it's the ALT and windings=RARE, or the Reg/Rect.....most likely. See the products Review/eval forum for Geezer's Reg/Rect unit, great product, and lifetime guarantee!
T.C.

PS, hope you got some sleep!

[Ken Talbot]

When the electrics on these bikes start to "work sometimes and not work other times" it is time to do an end-to-end cleaning of every electrical connection on the bike. You've got 25+ years of corrosion build-up to get rid of. Have a look at the picture links in this thread about electrical gremlins to see just one little spot that caused me a couple of years of aggravation on SWMBO's 'H.

[skids]

Re: Headlight problems

9v at idle will happen with the headlight on and the battery running down because the charging system is not keeping up...

Originally posted by HobbyMan
The srange thing is that when I measured the lead to the solenoid from the alternator, I got a lower voltage than normal. The engine was running and It was reading around 9V. I

[HobbyMan]

Well I checked and cleaned the connections behind the fuse pannel. I did not have time to check the rec/reg today but will be doing it soon. THere was a light layer of corrosion on the terminals that I cleaned. It wasn't much but it couldn't have been helping. I need some time to ride around and test it out, of which I have been lacking. I will also be checking out other gremlins soon. BTW: this is my 100th post, thats cool.

[HobbyMan]

OK, I finnaly did it. I tested the reg/rect and #8 diode is shot. It is passing current when it is supposed to shut off. The voltage regulator, while the engine is running, has a severe drop in voltage when the RPM is increasing above 2000 RPM, it drops down and then increases again. So I guess I will be putting a new unit in. Thanks everyone for the help!

[Pat Kelly]

Hobbyman,
Did your tach stop working when the headlight went out? Also, did the insturment lights still work?

[HobbyMan]

No, the tach and lights have always been ok. If the lights are going out and the engine is quitting, it may be the connector that runs all of that stuff from the hot side of starter relay. Its that one big wire with the single connection near the top of the battery. Most of the time, those get corroded and the plastic is brittle. Try wiggling it. I would probably put geezer's unit in even if the old one isn't bad. I like it soo much better. It keeps all of my signals blinking at idle and it starts better.