Dead 1990 k75s.. Please help :(

[farquand]

Where to begin... I suppose I shall begin at the beginning. First there was the Big Bang, which was big, but not much of a bang. Those astrophysicist types actually like to call it "the Inflationary Moment" I believe. Ok, maybe that's too far back...

So a few days ago I had some difficulty starting my K-bike after refueling. It turned over for an inordinately long time, and then just quit turning. So, I released the starter button gave it another try, and again lots of turning over, but no start and quit turning. So, I try again this time more turning over, and then BEHOLD it starts. I rode it home, which was about a 50 mile ride, and I get home, park it in the garage, and shut it off; wait a few minutes, turn it back on, hit the starter, and it starts right up without any issue. The next morning I go out to the garage, turn it on, and it starts right up, again without issue, so I ride to work, again about 50 miles. After work I go to start it, turn the key, and hit the starter button, and I get half a turn of the engine, and everything goes black. No headlight, no instrument lights, no nothing! Now when turn the key I get a whining sound coming from what I believe is the horn relay (furthest one to the right in the first row of relays in the box), and the tach starts to climb, there is a faint glow from some of the instrument lights, and the clock goes blank for a second, but will slowly come back on, but no headlight, no turn signal lights, no horn, and most importantly no starter motor turny over.

I have not installed any aftermarket accessories, ever, and there were none on it when I bought it. I have checked battery voltage, which gave a reading of 12.56 volts. I have checked and replaced all the fuses, just in case. I have cleaned the ever loving hell out of the ignition switch. Now I am at a loss, and I am hoping some benevolent, or at least chaotic good BMW motor wizard will help me sort this out. Thank you in advance for your efforts, and advice.

[roninvt]

I think the load shed relay is next to/left of the horn relay.  It could cause some of your symptoms, ie., lights blacked out.  Swap it with the horn relay and see if anything changes.  How old is your battery? Could have some volts but dies under load of starting.  Give it a good charge...

[kioolt]

I believe that you have a starter problem.  This would cause your load shed relay to whine or chatter.  Since you have a voltmeter you should check the voltage at the starter terminal.  Ideal voltage without the starter button pushed is 0v.  I believe that you will find much higher than that.  This would indicate a starter problem.  One thing you can try is to put the bike in gear and roll it backwards just a little.  This will cause you starter to get rotated a little and may make your headlight come on.  If so this would be an indication that the starter needs servicing.  Maybe just a cleaning and maybe brush replacement.  You could also try tapping on the starter.   Even if you get it started by doing either of these methods I would service the starter.

Please make sure all of your battery connections and your main ground cable to the transmission connection are good before doing the above checks. 

[farquand]

I believe that you have a starter problem.  This would cause your load shed relay to whine or chatter.  Since you have a voltmeter you should check the voltage at the starter terminal.  Ideal voltage without the starter button pushed is 0v.  I believe that you will find much higher than that.  This would indicate a starter problem.  One thing you can try is to put the bike in gear and roll it backwards just a little.  This will cause you starter to get rotated a little and may make your headlight come on.  If so this would be an indication that the starter needs servicing.  Maybe just a cleaning and maybe brush replacement.  You could also try tapping on the starter.   Even if you get it started by doing either of these methods I would service the starter.

Please make sure all of your battery connections and your main ground cable to the transmission connection are good before doing the above checks.

So when you say "at the starter terminal," are you referring to the terminal in the combination switch, or at the relay?

[Scott_]

I believe that you have a starter problem.  This would cause your load shed relay to whine or chatter.  Since you have a voltmeter you should check the voltage at the starter terminal.  Ideal voltage without the starter button pushed is 0v.  I believe that you will find much higher than that.  This would indicate a starter problem.  One thing you can try is to put the bike in gear and roll it backwards just a little.  This will cause you starter to get rotated a little and may make your headlight come on.  If so this would be an indication that the starter needs servicing.  Maybe just a cleaning and maybe brush replacement.  You could also try tapping on the starter.   Even if you get it started by doing either of these methods I would service the starter.

Please make sure all of your battery connections and your main ground cable to the transmission connection are good before doing the above checks.

So when you say "at the starter terminal," are you referring to the terminal in the combination switch, or at the relay?

He's referring to the terminal connection actually at the starter......

[rbm]

Your open circuit battery voltage may look good but under load, it may drop below 10V indicating a dead battery.  Measure the battery voltage when cranking (don't crank the engine with a dying battery as you risk welding the contacts on the starter relay).

Another suggestion was a dirty starter that needs servicing.  The ground return for the bike travels thorough the starter and carbon from the motor's brushes causes grounding problems, leading to the symptoms you have.  There are many tutorials on how to remove and clean the starter.  Use the search function.

[Scott_]

Another suggestion was a dirty starter that needs servicing.  The ground return for the bike travels thorough the starter and carbon from the motor's brushes causes grounding problems, leading to the symptoms you have.........

RBM, didn't you meant to say that the "ground return for the load shed relay travels thru the starter......"

[kioolt]

Another suggestion was a dirty starter that needs servicing.  The ground return for the bike travels thorough the starter and carbon from the motor's brushes causes grounding problems, leading to the symptoms you have.........

RBM, didn't you meant to say that the "ground return for the load shed relay travels thru the starter......"

That's absolutely correct about the load shed relay's ground return.  There is a lot of misinformation about the way the load shed relay works and also about what is grounded through the starter.  The ONLY thing that is grounded through the starter is the load shed relay.  Unfortunately when you loose this ground for the load shed relay the bike will go bonkers (technical term).  You are actually loosing the hot or plus side for your accessories, lights, etc when you loose the return ground through the starter.  Eventually your bike will not even turnover until you service your starter.

[rbm]

Yes, I did.  Thanks for correcting me.