Author Topic: '85 K100RS headlight inop  (Read 1718 times)

Offline Duckbubbles

  • ^ Motobrick Curious
  • Posts: 56
'85 K100RS headlight inop
« on: July 02, 2023, 08:39:25 AM »
Just finished a major service, all fluids, valve clearance check.  Did not mess with anything electrical.
Before I dive into it I want to see what suggestions the brain trust here might have.
Turn the key on.  The headlight does not come on, but the high beam indicator is on and stays on no matter which position the left switch (high/low/flash) is in.  Start engine and no change- no headlight.  I do have a euro headlight switch to turn the lights on or off.
I am leaning toward the load shedding relay but the high beam indicator has me baffled.
It's possible that both filaments are broken in the bulb, that that would not explain the high beam indicator.
I plan to get into it in the next couple of days, starting with checking voltage and ground at the headlight connection and go from there.

Frank
  • Austin, Texas USA
  • 1985 K100/1100RS
'85 K100/1100RS 40 years, 331,000 mi.
'23 R1250RS
'03 R1100S BCR #6/200
500,000+ BMW miles

Offline Scott_

  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 2242
Re: '85 K100RS headlight inop
« Reply #1 on: July 02, 2023, 09:49:52 AM »
Well, from what I see in the schematics, power from the battery goes thru the LSR before it goes to the left hi/low light switch.
The power goes to the left switch 1st to allow high beam flash-to-pass independent of the eruo on/off on the right switch for normal lighting use.
As far as the high beam dash indicator, the power for it starts at the hi/low switch, then to the connector for the extra alarm system, then to the dash cluster.

  • My Garage
1995 K1100LT 0302044
2017 FLHTK Ultra Limited
1997 K1100LT 0302488 (R.I.P.)
1997 R1100RT ZC62149(sold)
"One who does not ask questions is ashamed to learn" Danish proverb

Offline The Mighty Gryphon

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  • Posts: 6843
Re: '85 K100RS headlight inop
« Reply #2 on: July 02, 2023, 10:53:57 AM »
Crap!  I had that same problem exactly, a couple months ago when I took my K100rRS out of storage.  But right now I can't for the life of me recall what caused it beyond that it was in the fairing.  Will think about it today and get back if I remember.

All I can suggest is that you may have disturbed the connector on the back of the headlight.
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline Duckbubbles

  • ^ Motobrick Curious
  • Posts: 56
Re: '85 K100RS headlight inop
« Reply #3 on: July 03, 2023, 11:00:56 AM »
Gryphon, you are Mighty as you called it!
I spent some time yesterday looking at the schematics and (overthinking as usual) convinced myself that the problem must be in the electrical box.  Today I took the bike apart and started checking grounds and power at the load shed relay and bulb monitor. Couldn't find anything wrong.  WTF!
Decided to check the plug at the bulb and, lo and behold, I had power, high and low beam, and ground where they should be.  Plugged the bulb back in and everything works as it should.  It's been years since that connection was tampered with so I suppose a little corrosion was blocking the connection.
I said in my original post that I would check the bulb connection first and I would have saved myself a lot of work had I listened to that!
I just need to ride it around a while to get it good and warmed up and do a final throttle synch and it will be complete.
Thanks for the responses to all you guys.

Frank
  • Austin, Texas USA
  • 1985 K100/1100RS
'85 K100/1100RS 40 years, 331,000 mi.
'23 R1250RS
'03 R1100S BCR #6/200
500,000+ BMW miles

Offline The Mighty Gryphon

  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 6843
Re: '85 K100RS headlight inop
« Reply #4 on: July 03, 2023, 12:21:33 PM »
Thanks for the kind words.  If it hadn't just happened to me, I would have never had a clue as to the cause.
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

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