Alternator?

[Mgfever]

Just started my 91 Interstate this morning. The voltage was at 11.8 before starting but after letting it run for a few minutes, went back to check it out and my voltmeter was reading 8.0 volts. Thinking it was a problem with my meter but then I noticed my headlight wasn’t on. Shut it down and just dead. Is this a classic alternator failure or should I be looking for something else?

[DenverWinger]

Thinking maybe the starter button got stuck, this would cause the headlight to be off and starter likely drained the battery.... With engine idling the starter motor would just be free-wheeling.

[4given]

Thinking maybe the starter button got stuck, this would cause the headlight to be off and starter likely drained the battery.... With engine idling the starter motor would just be free-wheeling.

Hard to believe you wouldn’t hear that.

[Mgfever]

Well, not thinking it was a starter or an alternator issue. I got it on a charger for awhile and then started it again. At first it went up to 13.4 volts but then bounced down around 11.8 While messing with the wires on the starter solenoid I noticed that sometimes it would then go up or down so it may just be a wiring issue. I’ll explore a little more and then let you know what I find out.

[DenverWinger]

Maybe a hairline crack in the 55 amp Dogbone fuse. Charging current has to pass thru that fuse.

[Mgfever]

Thanks. I’ll need to checkup on that.
Checked the fuse and it was OK but I noticed there was some corrosion around a couple of the connections. Pulled them all and cleaned up the contacts, made sure all were tight and everything now seems to be fine. Par for the course for a thirty year old bike!

[Swagonmaster]

Also possible to have very worn brushes in the alternator that are right on the verge of no contact. It will charge as long as they touch and then just quit. If you can catch it when it fails to charge and rap on the rear of the alternator it might rattle the brushes and restore contact temporarily, would prove the cause of the problem.

[Mgfever]

Well, fixing the corroded wires didn’t help so decided to pull the alternator and check it out. Sure enough the brushes are worn all the way to the holes. Haven’t ordered the brushes yet. I’ll need to check the archives for sources and I suppose I should also get the rubber isolators.

[MikeB]

You could most likely go to any Alternator repair shop and find brushes that will fit perfectly.

[Earl43P]

https://cyclemax.com/inc/sdetail/gl1500 ... 4102/46303 Part number 31101-MN5-005

I replaced mine (on my Valkyrie IS) with little difficulty. Be careful moving the windings out of the slots when rotating/pulling the isolator plate, but it's a pretty straightforward job otherwise.
Might want to leave just a little bit longer pigtail on the new brushes. I found that mine had worn through one brush's hole and its travel was limited by the pigtail length.
The spring would have let it wear further with a longer pigtail. Keep that in mind when soldering the new ones in. Add ~1/4" of pigtail.

Mine was done at 96,xxx miles on an Original Installation and the alternator had not failed yet (last year's preventive maintenance).

[Wildwilly018]

When my alternator went a a couple or so yrs ago, I couldn't find anyone who would or could fix it or find parts here in Ontario Canada. So not to waste riding time, I ordered another one and put old one in box on shelf to add to my collection of broken bike parts lol. Have had no issues with this one and added a volts gage to my 88 so I would be stuck stranded again not knowing something was out of sorts in my charging system.