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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Charlie Mullendore on May 02, 2023, 11:04:50 AM
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I've searched until my eyes were blurry and my brain hurt, and still didn't come up with an answer, so here goes...
New K75 owner. Purchased it from a friend for $500. Over all a nice bike, but has two issues that will need to be fixed. I'm a self-employed motorcycle mechanic, but my specialty is older "analog" Euro bikes from the '60s, '70s and '80s. Guzzis, Morinis, BMW Airheads, and an occasional Benelli, Ducati and Cagiva. I'm going to need some help with this "modern" BMW...
One reason I got it so cheap is in the subject line. When the key switch is turned to the "on" position, everything works except the warning lights and gear indicator, when the starter button is pushed nothing happens. If the kill switch is in the "run" position, the top fuse blows, but in the "off" position it doesn't.
I've only owned the bike a few hours, but did start cleaning connectors (ones near the rear brake reservoir) with Caig Deoxit, charged the battery (12.6 resting volts) and put it in 5th gear and spun the engine backwards to spin the starter backwards.
Any suggestions for a path forward would be appreciated.
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Welcome! Does your bike have heated grips? I had problems on two Bricks with the heated grips blowing fuse #1. The right grip heater gets the insulation worn off the wire allowing it to short to the end of the handlebar. Sliding the grip out a bit to the end of the bar will stop it.
The starter brushes and the ignition key switch are known to cause a lot of strange and intermittent electrical problems.
The starter brushes are important for providing ground for the load shed relay among other things. There are posts here describing how others have checked them.
http://www.motobrick.com/index.php/topic,4087.0.html
The ignition switch is also a source of weird electrical stuff. The contacts are very sensitive to dirt and corrosion.
http://www.eilenberger.net/K75S/IgnitionSwitch/
There is a set screw holding the switch together that is sealed with red Loctite. It needs a cautious application of heat with a heat gun to soften the Loctite to make removal possible.
The grounds are important, there are a bunch of them under the tank attached to the frame backbone. Make sure they are nice and clean and tight.
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The #1 fuse only gets power when the kill switch is in the on position.
The following circuits run off of the #1 fuse:
Brake Switches
Clutch Switch
Instrument Cluster
Bulb Monitor Unit
Heated Grips
One of those circuits is shorting if the #1 fuse blows.
Take the right peg plate off to make sure that the rear brake switch wiring isn't grounding. If that gets pinched when the plate is installed then it will blow the #1 fuse.
To troubleshoot the heated grips as a possible short just put the HG switch in the middle position to open that circuit.
Since both the clutch switch and cluster are powered from the #1 fuse you will never get power to the start button with a blown #1 fuse. That's why it isn't cranking.
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Thanks to both of you for the input thus far.
The heated grip switch was in the middle position when the fuse blew, so it sounds like that rules them out.
The other issue the bike has (and the second reason I got it so cheap) is the rear brake wouldn't bleed out after the previous owner rebuilt the brake master cylinder. It could be that he's inadvertently pinched the wires with the right peg plate. It started and ran fine until he was doing the brake work, so this sounds highly likely.
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Success! icon_cheers I unplugged the rear brake switch connector, put in another fuse, turned the key on. Warning lights now work, engine cranks and started! Woo hoo! Easiest fix ever... Thanks Frankenduck!