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Author Topic: Eerie Electrical Gremlin 1988 k100 LT  (Read 9293 times)

Offline kylemb

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Eerie Electrical Gremlin 1988 k100 LT
« on: April 20, 2016, 12:54:36 PM »
last year i bought this 1988 k100- 140,000 miles. kept up well and in great shape mechanically and otherwise... i started noticing some odd electrical gremlins such as the cooling fan would cycle on/off with the blinkers! i would randomly lose power around 3,500 RPM? (can't remember exact RPM) until i restarted the bike... of course i checked my connections, grounds, used some electrical lube etc...
last july i had a totaly melt down. on the interstate my tachometer stopped working and i had a battery light on. i tried restarting the bike on the fly and it wouldn't start... eventually i had to push the bike off and thats when smoke poured out from my right handlebar and under the gas tank. quickly shutting off the bike & towing it home i disassembled what was now a worthless piece of crap wiring harness that was totally fried.

after heavily some intense googling and research i tracked down a gentleman and commissioned him to build a new loom for the bike. having replaced the wiring harness with this new one TODAY THE BIKE STARTED UP AND IT SOUNDS AMAZING. Here is a link if you'd like to hear it:

https://goo.gl/photos/2wV5LxRqN1NvUboy5

unfortunately i found some gremlins!
everything checked out except the blinkers, the hazard lights, and low beam would not work. i let the bike idle until the fan came on and then i tried toggling the high / low beam and i noticed the high beam was causing the fan to come on! toggle to low and the fan would turn off, toggle to high beam and the fan is back on!
what the hell is going on with this fan gremlin? all the electricals have been replaces: the entire harness, the fuse box and everything inside, the switches, etc!

i need some k100 guru support so i can get this thing back on the road before i miss this summer too!
thanks in advance.

-K

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  • North Alabama
  • 88 K100 LT // 85 K100 RT

Offline Laitch

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #1 on: April 20, 2016, 01:15:55 PM »
Do the three "No Start" procedures in the Workshop section. Clean and reconnect securely your four pin connector under the tank as well as the ignition switch plug under there, too. Please get back to us with the results.
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  • Along the Ridley in Vermont.
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Offline rbm

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #2 on: April 20, 2016, 02:03:49 PM »
So, is this "new" loom a complete from-the-ground-up redesign of the BMW loom?  Or is it a refurbished BMW loom, with all the same connectors and connections?

If the loom is stock, it might be a problem with the temperature sensor wiring.  The fan comes on because the tep relay thinks the engine is overheating.  It senses engine temps from one side of the temp sensor.  As the resistance of the sensor decreases, a threshold is reached when the temp relay turns on the fan.  You might be getting an accidental ground signal to Pin 31 of the temp relay.

Isolate the problem to either the temp relay wiring or something else.  Pull the temp realy and try your lo/hi beam experiment.  If the experiment fails, the problem is in the temp relay or relay wiring.  If it passes, the problem is elsewhere.
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  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline kylemb

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #3 on: April 20, 2016, 02:33:58 PM »
Quote from: rbm on April 20, 2016, 02:03:49 PM
So, is this "new" loom a complete from-the-ground-up redesign of the BMW loom?  Or is it a refurbished BMW loom, with all the same connectors and connections?

If the loom is stock, it might be a problem with the temperature sensor wiring.  The fan comes on because the tep relay thinks the engine is overheating.  It senses engine temps from one side of the temp sensor.  As the resistance of the sensor decreases, a threshold is reached when the temp relay turns on the fan.  You might be getting an accidental ground signal to Pin 31 of the temp relay.

It had been built from the ground up as far as wiring goes. Everything in the fuse box i believe is either from my old bike or new replacements. The wiring connectors are all refurbished or new and added on to the new wires.

At this point it looks like i need to do those 'No Start Procedures' & clean out the starter for sure.
I should be able to share results by tomorrow.
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  • North Alabama
  • 88 K100 LT // 85 K100 RT

Offline kylemb

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #4 on: April 20, 2016, 09:13:32 PM »
Good news: blinkers, headlights (both high & low) and hazard lights all work!
Looks like the cable was loose under the blinker relay and that was it for the hazards too. i wasn't using the correct switch for the low beam.
so that just means turning the headlight ON was toggling the cooling fan somehow. maybe a bad relay? but how is the headlight interfering with the temp relay?


something else i noticed: when i kick the throttle fast the engine hesitates and nearly cuts out. ( https://goo.gl/photos/S7DpD1TpfGmDST3M7 ) not sure if it just needs to run or what.

also checked and cleaned the starter. looks amazing inside. Where is that Gremlin?
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  • North Alabama
  • 88 K100 LT // 85 K100 RT

Offline johnny

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #5 on: April 21, 2016, 03:27:19 AM »
greetings kylemb...

no instant gratification at 9 hundert rpms...

you gotts to be up at 7 thou or higher for instant gratification...

j o
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  • :johnny i parks my 96 eleven hundert rs motobrick in dodge county cheezconsin  :johnny

Offline kylemb

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #6 on: May 20, 2016, 11:08:09 AM »
This will be the second time cleaning the starter for hopes that this is the issue for the gremlin. Again, when the radiator fan turns on and I activate the blinkers, the fan cycles on/of with the blinkers. I agitated this symptom the other day and the bike shut itself off. It wouldn't restart until I reconnected the battery.

Anyway, here are some detailed photos of the starter:

https://goo.gl/photos/QdsX4PNnMZieUvLk8
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  • North Alabama
  • 88 K100 LT // 85 K100 RT

Offline kylemb

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #7 on: May 23, 2016, 03:38:47 PM »
i replaced the brushes and the gremlin still lives. check out this video of all the bugger the fan experiences. could it be the fan is going out? the temp relay? the load shed relay? any other relay?

https://goo.gl/photos/pmgo6BYnRYrsErn36
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  • North Alabama
  • 88 K100 LT // 85 K100 RT

Offline Laitch

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #8 on: May 23, 2016, 06:08:17 PM »
Quote from: kylemb on May 23, 2016, 03:38:47 PM
. . . check out this video of all the bugger the fan experiences . . .
I couldn't find any video at that link, kyle.
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline kylemb

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #9 on: May 23, 2016, 06:10:20 PM »
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  • North Alabama
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Offline Laitch

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #10 on: May 23, 2016, 06:18:10 PM »
Thanks. Looks like I just needed more patience for it to load.

Is the charge light pulsing like the fan or is it off completely?
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  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline kylemb

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #11 on: May 23, 2016, 06:26:39 PM »
Quote from: Laitch on May 23, 2016, 06:18:10 PM
Thanks. Looks like I just needed more patience for it to load.

Is the charge light pulsing like the fan or is it off completely?

Charge light is completely off.
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  • North Alabama
  • 88 K100 LT // 85 K100 RT

Offline rbm

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #12 on: May 23, 2016, 07:50:07 PM »
It appears that the fan is functioning as designed, meaning it turns on and off as instructed by the temperature relay.  However, there is a part in the video where the fan attempts to turn on and starts up slowly and hesitantly.  Here it seems that the motor is trying to overcome severe friction.  I'd also wager that the fan speed you are hearing, pulsing in synchro with the blinkers, is related to this friction in the fan.  The motor will attempt to draw extra current to avoid a stall condition.  This draw is starved with each signal flash as current is diverted to the lights.

I took another look at the video and the fan seems wrong.  From the angle of the video, it looks like there is too much space between the blade hub and motor.  I think the fan blades have slipped on the shaft.  That could be the friction it is encountering.  It's not unheard of; one particularly nasty fan failure is for the fan axle to slip forward and to drill a hole into the rad, requiring a radiator and fan replacement.

I'd first remove the fan and get it replaced.  No point in trying to save money by servicing it because it's on its last legs.  There are good posts here and else wheres about using a modern SPAL fan replacement.

Also, just saying.  You're probably going to be questioned a lot about the custom loom.  No one can say how faithfully this wiring was constructed, or even if it followed the OEM loom verbatim.  Any electrical problem will always come back to questioning whether the loom is correctly constructed or not.
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  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline The Dude

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Re: Eerie Electrical Gremlin 1988 k100 LT
« Reply #13 on: May 23, 2016, 08:49:59 PM »
Ye h ,it's a bugger alright.Seen the vid.
But...the fan is a piece of shite.Mine hasn't worked for decades possibly only ever coming on the once,no yellow light either...(I vaguely remember)but I ride fast and don't sit in trafic tooooo long so I've got away with no overheating...or any need for the fan to keep itself going.When I got around to taking it off ,some thirty years since...,the bearing just behind the blades was compleaty seized so I squirted some oil in there and did the back and forth thing and for three days and four nights it told me that I wasn't going to put it back in and I was happy to just have nothing there(more free air flow).well..the blade span up, free as ,on the forth day, brushes and commutator as new,so I put it back...and made sure ,by using a hose clamp,that it wouldn't migrate into the radiator fins,cos the three clips ,I didn't trust.I can spot shit happening before it does,after all my years....

What I'd do if I was going to sit in trafic for more than a minute would be to isolate the fan with a manual switch( there's some clues on this site for that)or just switch the motor off,like those newfangled stop start vehicles.
All the best,you've nearly got all that smoke back inside the wires,as it is.
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  • Auckland, New Zealand
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On my second millionth km.give or take a hundred k Kay's.
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All the best!
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