I am new to K bikes. I've had and ridden this 1985 2V K100 for about a year. I noticed though that while all of the electrical seemed to work marginally UK, I had to purchase a trickle-charger in order to keep the battery up and that the charge light would stay on for a long time after a ride of any length. I purchased a new battery last fall but when I went to install it I noticed that even fully charged as soon as would start to re-connect the wires the charger would go to red (light) indicating it needed a charge. since the ignition and kill switch were off this implies a short to me. I waited until now to tear into it .( the bike's electrical system has been unconnected since fall). What I discovered was that 2 main wires on the positive pole connect without a problem but the third going to a little Green, 1" cube box, under the seat which from the owners Manual diagram should be #43 the starter relay. Nothing seems to be wired right though. For instance one wire goes to ground and in the diagram nothing should be going to ground (#30) Is that correct? another wire #85 is spiced into a wire going to the rear brake-light. #87 goes to the battery + terminal #86 is cut off and no wire anywhere in sight #87b has nothing on it. Nothing appears to be fused. What is amazing to me is that the bike starts and runs puts on the right trouble light until the brakes are pressed and turn signals work, starter motor works. the alternator is in question since it did not seem to be putting back a charge when I was riding it. I don't now where to look for: Load shedding relay, or how to get into the back of the fuse box. Maybe I'm asking too much but can any one help. I've worked on lots of cars with good success but no bikes. I really like this machine though and am hesitant to re-connect it the way it was. It may already be damaged.

Twcarlist,

Sorry, I don't have the original owner manual and cannot follow your explaination with the #s
Go to the download section of this site, and get the color wiring diagram. It's a lot easier to follow the circuit. The starter relay is in the tray under the tank. Unless somebody had modified the electrical, the small 1" square relais are for the horn, Fuel injection and load shed relay.


NOTE ON STARTER RELAYS:

If you try starting your bike with a weak battery, you take a chance to burn your starter relay.
This is easy to understand: Amps = Watts/Volt
The starter is 700 watts. at 13 volts (battery fully charged) the starter will pull 54 Amps. If the battery is down to 10 volts, the same starter will pull 70 Amps and you have a good chance to burn the contacts of the relay (they will stick together). The starter will continue to turn until you disconnect the battery. During this time, the starter will continue to drag your battery down, and if you get to 6 volts, the amperage will be around 115 amps.
A starter relay cost $140 at BMW, but only $49.00 at EuroMotoElectrics (part # BOREL-K008).
I experienced this problem on one of my K bike. After I took a small step to minimize the damage. I installed a kill switch. It's only a 30 amps rocker switch installed on the negative side of the battery .

If you have access to a voltmeter, connect it to the battery with the engine off and then start it. After you start the bike the voltage should increase with revs eventually reaching over 14 volts. If it stays around the 12 volt mark or even drops, you're not charging the battery. If it rises well when the engine is running but drops rapidly below 12 volts when turned off you may have a faulty battery. If you want to check for current drain when the bike is turned off, most of even the cheap multimeters around will have a 10amp dc current range as well as voltage so you can disconnect the positive battery terminal and connect the meter between the terminal and the main 12volt lead and measure the current drop. Unless you have an alarm / immobiliser on the bike the current when the bike is off should be extremely low. If it isn't, you may then have a partial short somewhere. Remember not to try and start the bike while the meter is measuring amps as no domestic multimeters that I know of can deal with 60+ amps across the meter.

Barnesst, you have very good troubleshouting skills. This is an excellent way to check your circuit. I just have to add one thing:
When the ignition is off, unless you have an alarm system (as you pointed in your reply) the only thing that should drain on the battery is the clock. If you disconnect the instrument cluster, the drain on the battery should be ZERO.

I am not sure if this has been mentioned but the fuel pump- fuel injection relay is on the LHS of my bike and has five connections as opposed to the picture above. It is apparent that workshop manuals (including the official ones I use every day) are to be taken as a rough guide as opposed to the definitive resource we would like it to be.

Regards,

Phil

Hi Folks,
Phil hits on an interesting point, when we were/are working through Roy's problem it became apparent that there are two circuit diagrams for his bike at least, on one they show this very relay with one terminal and on the other it is shown with an extra terminal as Phil has actually got installed. The reason for the extra terminal seems to be that at least in some bikes (Phil's certainly) they split the power off the supply input terminal into two outputs where one supplies the injectors and one supplies the fuel pump. In the other version the one output contact supplies both.
Regards,
K-BIKE

Hi Folks,
With regard to testing for current drain a good technique that is a bit safer on one's pocket than a current meter is to use a test light in series with the battery lead. The type where a filament bulb in a holder has either a wire and a probe or two wires, either type is fine. It is worth making one up if you don't have one.

Why I say it is safer on the pocket is if the current drain exceeds the full scale deflection of your ammeter the ammeter will be killed stone dead. If you use a test light then the current flow is restricted by the impedance of the lamp filament. A glowing light is easy to find/see as well.
Time for Confession
I have, when doing this test on a pal's car with his meter to measure current drain with the ignition turned on, after connecting his expensive ammeter in circuit I carelessly turned the ignition switch too far when turning it on . As I went past the Ignition On position of key to the Start position the meter pointer tried to do a 360 round the dial in its case. At that point in the proceedings the high pressure smoke escaped from the meter unit and hence due to the loss of the smoke would not work any more :-) so BTDT!

Now I use a test light at least at the beginning of the test procedure when hunting leaks.

Just as an aside (no BMW M/C content) when testing older vehicles with a self winding mechanical clock like the old Kienzle units, they were spring driven and as they ran down they automatically closed a contact internally and a little motor inside rewound them. If you have one of those after connecting the test light in circuit with the battery and battery lead just touch connect the battery terminal direct onto the battery for two seconds to allow it to wind the clock, from memory they rewound themselves about every minute.

Back to bikes with the test light in circuit if the test light does not light, (having previously confirmed that it works by putting it across the battery to see it light) then you know that either there is no drain or there is such a low drain it will not light the light.

Try moving the handle bars lock to lock watching the light to see if it flickers on, showing a cable to cable short. If nothing shows then it is safe to put a meter into circuit. Meters can be connected two ways in circuit with the battery lead either as an ammeter or a volt meter. When connected as an ammeter one can see how much current is flowing, as Bert says the clock has a small drain as does any theft alarm but if you have a drain of more than 25 to 50 milliamps including clock and alarm you have a short circuit drain on the system which will flatten the battery. As Bert says above on our bikes with the clock disconnected the drain should be ZERO. I put one of the single LED voltage meters on my bike via an ignition switched circuit so as to be able to see that electrically things were OK voltage wise. As commented above by barnesst you will have little or no output on your alternator at tickover and will be discharging your battery only when you are revving at normal driving revs will you be putting power back into the battery (assuming the alternator is working).

Once you have verified the current drain is there pull out and replace fuses until the drain stops, then you have identified the circuit causing the drain. Then you have to go through that circuit identifying what is on the circuit and eliminatiing the components one by one, Bert's EXCELLENT colour circuit diagram will almost certainly be very helpful there.
Regards,
K-BIKE