Ignition short on 83 r100s.

[Ridercam]

I really miss riding my bike as it has been nearly 6 months since my last trouble free ride. She started giving me some starting problems over the early summer and i put her Into the back of the garage to deal with other life's matters in July. I have had her for 25 years and have done most of the basic maintenance myself. Work has slowed for the season and life are pushing me a bit. I love riding this time of year and now really need some saddle time to reset my unsettled mind.

So this leads me to asking where do I start to trouble shoot this. I have removed the s fairing, replaced the multimeter batteries and have a back and white electrical diagram from the Haynes shop manual. I will admit my weakness on this long no held bike is the electrical. My good r100cs girl is shorting out when I turn the ignition. My fuses are good and the battery is less than 2 years old and fully charged. where do I start my electrical detective work from here?

[ME 109]

More detail on what is shorting. Where is it shorting? What are the symptoms?
Are there sparks? smoke?

Clean the cable connections at the battery.

[Airbear]

Agree about more info required.
With the headlight out and the tank off can you see any apparent damage to wires or components?
What actually happens when the ignition is turned on?
Do the idiot lights come on as they should?
If so, what happens when you hit the starter button?
Anything else of interest?

ps: Yep, saddle time is good. Saddle time in the long light of an autumn afternoon is special.

[Ridercam]

Once the key is turned to the "on" position the bikes entire electrical system goes off. No lights of any kind. There is no smoke, pop or click. Once I turn the ignition key to the off position the bikes the clock again works. I may be jumping to incorrect conclusions but I was thinking the on/off contact handlebar switch may be the problem area. Might disassemble and/or clean that switch first as well as the relay under the tank too.

[ME 109]

Once the key is turned to the "on" position the bikes entire electrical system goes off.

Is this to say that when the key is off, the electrical system is on???

Assume there is no power to starter?
Check battery connections for poor contact. Or fuses in headlight shell.

[jagarra]

Maybe the system is not even turning on. Sounds like it cannot handle load. I would start by cleaning all ground connections to frame.

[barryh]

Before assuming it's a short circuit, measure the voltage at the battery terminals while turning on the ignition. It would be normal to see a small voltage drop caused by the ignition load so a drop of half a volt or so is OK. If you see a big voltage drop then big currents are flowing as you would expect from a short circuit.

[Airbear]

I don't think it is a short circuit. It is an almost-open circuit, meaning a bad connection. With a very small demand like the clock enough current can flow but with a bigger demand the corroded connection will arc, create a little bit more corrosion and drop out. In a dark shed you may even see the little spark as this happens. The first thing I would do is remove the battery connections, clean and re-tighten. Next to check would be the connection of the negative battery lead at the gearbox, then the connection of the big red cable at the starter motor and so on. With the ignition in the ON position you can just wiggle the connections and see if the idiot lights come on.

One of these is very useful - a few bucks at your local auto store:



The alligator clip goes on a cylinder fin and you can probe around testing that you have a voltage where you should. For instance, is there a voltage at the red wire attached to the ignition switch, then the green wire and so on.

[Ridercam]

Ran the test with battery. The battery dropped out to near zero once the ignition was engaged. Once off, the clock starts to work as load is so low. My first move will be to replace the gel BMW battery which I now realize is three years old and has been stressed with a few times of critical wear down. I will then follow the grounds to ensure no shorting, will check various contacts, running lights, other instruments as well as I may have neglected to check/clean them over the years.

[ME 109]

Did you check with a voltmeter on the battery negative and positive posts and not a wire or terminal attached to the post? Don't buy a battery for nothing!
I just replaced my approx 7 year old motobatt on the weekend. $235! ouch. I did the tests with a volt meter to assess load capacity, and charging and cabling.
The first thing to do is check connections at the battery. Loosen, clean and reattach. Five minutes work.