Headlight and cluster dimming while riding

[Yocharles114]

Hello,

I am new to this forum. I just bought a k100 1985 in great condition! While riding it at night the cluster and headlight are dimming at intermittent rpm. It goes to full brightness when I give it full throttle.i also had trouble starting it last night, starter was not engaging but i could hear the pump running…

Anybody has an idea?

[Ingo]

Alternator. What mileage?

[daveson]

While in a high gear and rolling backwards, drop the clutch. Do it a few times. If it now works better, that's a sign that the starter commutator was dirty or that the starter brushes are worn.

[Laitch]

Ingo and daveson have come up with good ideas.

I caution you to avoid embarking on the battery-alternator death march by first removing the battery and taking it to a NAPA up your way where they will load test it for free and let you know if it needs to go to hospice or can be reinstalled. Let us know what they indicate before plunking down loonies for a new one. If it's good enough to reinstall, the source of your problem could be the alternator. It also could be the battery cable terminals are corroded/loose, the battery ground cable attached to the transmission is dirty/loose, or the cable from the alternator to the battery is loose, among a few other conditions.

You'll likely determine some of that when you remove the battery for testing. There is a workshop manual and also a rider's manual downloadable from this page.

[Mambo5]

I would check out the very good cleaning ignition switch notes on site. I had a similar problem, replaced battery etc, and traced it to the switch. Don Eilenberger wrote an excellent post if you have a look… http://www.eilenberger.net/K75S/IgnitionSwitch/