This story is slightly long winded so please bear with me.

I have been enjoying my 1985 BMW K100 for the last three years and near the end of last season the bike just wouldn't start anymore. After a glorious 1800 km trip through northern Ontario and down the Bruce Peninsula I stopped for gas 80 km from home and my bike would not start. I couldn't bump start it, I could not get it to turn over so, I managed to rent a truck and bring it home to the garage where it sat and waited.

I called my closest BMW dealership 100 km west of here and they had no idea what it could be as they had never worked on a K100. So I started with the cheapest component in the starting system which was the starter relay. It took two months to get it from Germany and it was an aftermarket component, due to the lack of availability of OEM parts for this model and year. So I had to wait till the spring to start working on it again. I installed the new relay and reconnected the battery then due to my absolute brilliance I wired the battery backwards and fried the positive side of the wiring. I then ordered a replacement wiring harness as once again it is impossible to get anything for the K100 so that took several weeks. I then spliced the wiring back together and alas once the battery is connected the battery light and clock turn on but will not start or even get a clicking sound from the starter but the fuel pump does turn on occasionally. The starter appears to work as a jump start from the battery positive side to the starter wire connection gets it to turn but no kick.

The battery is fully charged, I have checked and rechecked the harness and all is connected solidly but the battery light turns on as soon as the battery is hooked up, I have installed the old starter relay and the new starter relay with the same results repeatedly. I have taken the starter switch apart and cleaned it thoroughly and the same results once again. All the fuses are in working order so, now I am at a loss as to what to try next and I'm getting sick of seeing other people enjoy their bikes while I sit in a shed cursing at my bike.

What should I try next?

Thank You,

elementalfire

Are you stating that the alternator warning light is lit when the battery is connected but without the ignition switch being turned to On?

Next time you need to disconnect the battery to replace another component, just unfasten the battery ground cable from the transmission then wrap a piece of tape around its terminal so it doesn't contact metal.

What do you mean when you wrote "... I then ordered a replacement wiring harness as once again ... I then spliced the wiring back together ..."?  Are you saying that you ordered a complete wiring harness from some place, received it and then proceeded to completely swap the old harness for the new one?  Or are you saying you actually tried to splice and solder together parts from one harness onto the old one?  I'm not clear.

Mind you, having the alternator light come on when you connect the battery is not a good sign.

Does your  bike have an aftermarket speedometer/instrument cluster?  If you have the original instruments, does the green neutral light come on?  Does the gear indicator show a zero?

Does the starter spin when you push the start button?

Are all the fuses good?  You might want to replace them even if they look okay.  They are known to go bad with age.

Does the headlight go out when you press the start button?

Are all te ground connections nice and clean and tight?

How are the starter brushes.  Worn brushes and carbon dust will wreak havoc with the electrical system.

Least but probably not last, my used K-bike stalled on my first ride the day after I bought it. Turning the ignition to On and pushing the starter button did nothing, too. After scouting around the bike then reviewing the Rider's Manual, I checked the plug to the electronic fuel injection control unit beneath the tool box under the seat. It was not firmly connected because its latch wasn't holding it tightly. I pushed the plug into position, improved the tension on its latch then away we went—10 minutes riding time lost.

That's the only significant trouble I've had with the bike except riding it so often keeps me from accomplishing much.

When you hooked up the battery backwards you may have completely screwed yourself.  Electronics don't like to be hooked up backwards.  That plus side wire that you burnt didn't burn because it cares about polarity.  It was just the path for whatever was drawing such excessive current  As far as your starter problem, get a voltmeter and check your starter relay with it.  You should have 12 volts across the two small wires on it. By across I mean put one probe on one small terminal and the other probe on the other small terminal and turn the key on and press the start button.  If you don't have 12 volts at this point you need to determine if its the plus side or the negative side that is not working.  To do that put the plus probe on either small wire and the minus probe on a good ground.  Turn the key on and press the start button.  If you have 12 volts at this point then your problem is coming from your ignition control unit.  It controls the negative side small wire.

Alright, answers to the multiple questions.

1) I remove the melted portions of the wiring harness between the starter relay and the battery connection and the alternator. The I butt spliced the wires with appropriate sized butt connectors and shrink wrapped them.

2) The battery light and clock turn on as soon as the battery is connected. I have checked for parasitic bleed off from the amperage and I do not see any noticeable drop.

3) The instrument cluster is OEM and from all indications is original to the bike. The neutral light, choke light and all other indicators turn on when the ignition is turned on. The headlight does not fade when I press the starter button. I have disassembled, cleaned and reassembled the starter switch assembly. It was slightly dirty but was making contact easily.

4) I have checked the voltage across the starter relay and it displays 12 volts without the key in the ignition.

5) There is absolutely no kick from the starter when the starter button is depressed.

6) All fuses appear to be in good order, I have removed, checked a reinserted all the fuses.

7) If the ground wire isn't making contact with the transmission do I not run the risk of making the entire bike a shock hazard?

I am unaware of the status of the starter brushes but I do know that if I jump start from the battery directly to the starter it does turn over easily but no kick.

9) I removed the ignition coil cover to look at the coils and wires and everything seems to be in good order and connected well.

10) The ground connection at the transmission feels tight and shows no sign of corrosion or breaks in the wiring or sheathing.

Should I be looking at replacing the ignition control module under the seat?

Thanks to everyone,

elementalfire

possibly what you need to do  is measure the + terminal at the starter , ignition on , and start button pressed

if the voltage is lower than perhaps 10 volts at that time  you may have an issue of the starter relay

but you do need a very good earth wire from the battery to the gearbox lug - bolt , if that wire is lossy (incapable of carrying the amps required for a start )  a lot of things wont be working correctly during start conditions

btw the head lamps should switch off during start conditions (this is the power shed relay that does that )

you mentioned that the battery lamp illuminates as power is connected to the battery ?

that shouldn't happen until ignition is turned on

perhaps there is still some issues in the loom that you have repaired ?

just trying to offer some help at least

good luck

Point-Seven-five wrote:
Does the starter spin when you push the start button?

Does the headlight go out when you press the start button?

Are all te ground connections nice and clean and tight?

How are the starter brushes.  Worn brushes and carbon dust will wreak havoc with the electrical system.

If the starter is spinning but not engaging, suspect sprag clutch.  Not sure what is applicable to an 85 K  does it have a side stand switch? Have you tried pulling the clutch in?
Regards Martin.

elementalfire wrote:2) The battery light and clock turn on as soon as the battery is connected. I have checked for parasitic bleed off from the amperage and I do not see any noticeable drop.

3) The instrument cluster is OEM and from all indications is original to the bike. The . . . choke light turn on. . . when the ignition is turned on . . .

Should I be looking at replacing the ignition control module under the seat?

The clock should turn on when the battery is connected but as Charlie has indicated the alternator warning light should not be lit. Just having the clock on is enough to drain a battery after a while.

The choke light should not turn on unless the choke has been moved from its Off position to one of its two other positions.

You shouldn't be looking at the ignition control unit yet.

As Martin has observed, by your description the Sprag clutch component of your starter seems like it isn't working correctly. There are methods that might get it to work without major disassembly, especially if you can get your bike running by bump-starting it.

Seems to me tha starter relay is shagged. Put the meter across the t main terminals of the relay and you should see 12 volts then press the start button if the volts drops to zero the relay is operating if 12 volts remain the relay is not operating. It explains why the headlight does not turn off and that the starter turns the engine when 12 volts is directly applied.

It sounds like you are not getting the ground for the load she'd relay (from starter) so not even getting power to the starter relay to energize starter.

After reading your post #7, it seems to me that you much more damage to your harness than what is visible to you. The strange behaviour you're seeing can't be attributed to failed components like the ICU or starter relay. I'm thinking your original harness has internal shorts under the wrapping due to melted insulation caused by the reversed battery hookup. Consequently, you've not begun to address the problem by patching that bit of wiring you've done so far.

My suggestion is to purchase a new harness for your model year bike and do a complete replacement. That would be the easiest way to begin to solve this problem. The hard way will be to completely remove your current harness, disassemble it and fix what problems will be apparent once you get the wrapping off.

I did not see that you had connected the battery reverse polarity. I reckon you have fried the ICU, ECU and lots more of the harness.. and possibly the indicator relay. You wont have hurt any relays except maybe for the starter relay as that has a diode in it.
Replace the main harness and fuel injection harness plus the ICU and ECU. The ICU and ECU will not tolerate reversal of polarity.

Maybe yes, maybe no, Rick.  These are automotive electronic components commonly used at the time on Euopean cars as well as BMW motorcycles.  The designers would (should) have designed for load dumps and reverse polarity in the power supply sections of the ICU and ECU as those conditions are very common in automobiles.  They may well have survived the battery polarity reversal but the harness most certainly wouldn't have. The diode in the starter relay is reverse biased across the coil and is used as a snubber.  It may have been damaged since it would have been in a conducting state however, maybe it remains undamaged since the ground path for the starter relay through the ICU would have been off.  In the end, it's really hard to say what got killed and what survived.

I fixed on for a guy about 12 years ago Rob and AFAIK there is no protection or it didn't work.

Thank you everyone for your input, I will keep plugging(and unplugging) away at it. I have a new starter relay that I have installed and I get the same result as with the old relay. Battery light turns on as soon as the battery is installed. I am moving this week so I won't be able to get at it for at least a few more days. The aggravation continues.

robmack wrote:Maybe yes, maybe no, Rick.  These are automotive electronic components commonly used at the time on Euopean cars as well as BMW motorcycles.  The designers would (should) have designed for load dumps and reverse polarity in the power supply sections of the ICU and ECU as those conditions are very common in automobiles.  

I have an icu open here in front of me rob and I can confirm that it does have diode protection on the input supply like most of the circuitry on almost all the electronic components on the k bikes
I haven't opened an ficu yet but imagine it is the same
the gpi , temp sensor relay and flasher unit also have diode protection

the diode in particular in the icu , like many other bm electronics has a fuseable resistor in front of it .

like most items , it will become non functional until it can be serviced by a competent technician .

but definitely repairable should such a circumstance happen

just what i see in front of me

elementalfire wrote:Thank you everyone for your input, I will keep plugging(and unplugging) away at it. I have a new starter relay that I have installed and I get the same result as with the old relay. Battery light turns on as soon as the battery is installed. I am moving this week so I won't be able to get at it for at least a few more days. The aggravation continues.

 I had a problem  with starting  -lites worked but start buton was dead ,after much looking I discovered the flipper buton on the start buton was in the far  left position  in staed of the middle  position  I put it in the minle position all was fine  jim

lowboyjimmy wrote: I had a problem  with starting  -lites worked but start buton was dead ,after much looking I discovered the flipper buton on the start buton was in the far  left position  in staed of the middle  position  I put it in the minle position all was fine  jim

I am embarrassed to say that has happened to me recently.  Took about 20 minutes to spot it.

Which is the reason why whenever I rewire a bike, if possible I modify the loom so that the idiot lights go through the kill switch.  

You can't do it on a K-loom, bugger.

Point-Seven-five wrote:

lowboyjimmy wrote: I had a problem  with starting  -lites worked but start buton was dead ,after much looking I discovered the flipper buton on the start buton was in the far  left position  in staed of the middle  position  I put it in the minle position all was fine  jim

I am embarrassed to say that has happened to me recently.  Took about 20 minutes to spot it.

 when I got the bike  the flip switch was in the mid position  one  day I wondered what that was for  I flipped it  to the rite and  the bike quit I thought oh a kill buton flipped it back  started ir and  never touched it again , ididnt realize it had a far left position, probably  when I threw a blanket over it  it went left -bingo I had a problem , it took me longer than 20 min it bump into a solution
your not far from me , and I have seen your  responses to my problems before and a welcome note too thank you , im gonna try putting it in a higher gear and bumping it backwards  like the fellow  before you said  or taping on the housing   thanks   jim