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Headlight Switch Cleaning & Repair

Headlight (Hi-Lo) Switch Repair

By Don Eilenberger
April 1998

Folks – I know we’ve beaten it almost to death, butt – a few notes on an experiment I performed this weekend on my K100RT (’85).

As some may remember, I was running an 80/100 bulb in the K in the attempt to get more light where I need it.

I recently removed the 80/100 and found the inside of the envelope (bulb) had deposits on it – indicating to me that it was running at a lower voltage than designed for (halogen bulbs are designed to run so hot that the normal filament deposits are evaporated off the inside of the envelope back onto the filament).

Another thing I’d noticed lately is that my hi-low switch was developing a dead spot when switching from high to low or low to high. It also was stiffer to use than I’d remembered.

Figuring the switch was about to do a meltdown, I decided I had nothing much to loose by taking it apart and looking to see if I could find what was wrong. Or starting to go wrong.

CAVEATS: Don’t do this in the driveway (BTDT-WDIA). Don’t do it if you’re a klutz with tiny parts. Don’t do it if your switch is OK – it might not be when you’re done.

I unscrewed the switch from the handgrip (while parked in the driveway), unclipped the tie-wraps holding the cable in place, and put it up on my tankbag for dissection.

There are LOTS of little phillips (+) screws holding things together in the light switch. So I grabbed my magnetic parts holder thingie, and put it on the tankbag next to the switch.

It became obvious to me – that to take the actual switch outta the housing, first the plastic plate holding the wires in place gotta be removed (three screws – one of a different length). And then the horn and turn signal buttons gotta come off (more little screws).

CAVEAT: The horn button has behind it – a tiny spring AND a funny brass piece – which is not magnetic – and WILL jump right outta there onto the driveway (BTDT). Takes a while to find (BTDT), and the horn button only will work if it’s put back in (BTDT) the right way (BTDT). IF not installed, or not installed the right way – you have a permanent ON horn button (BTDT) which will annoy the neighbors as soon as you turn the ignition on (BTDT).

After removal of these two buttons, and 3 more screws (again, different length screws) – you can remove the switch from the housing and examine it.

Mine didn’t look ‘bad’ – but operating it – I could see the contacts which switch the hi/lo. And they were gunked up with dirt. Black sorta dirt.

I used some flammable/carcinogenic/bad-stuff electrical cleaner on the end of a rag with a tiny screwdriver inside it to clean them. I found it necessary to operate the switch lots of times before they started staying clean.

Note – they are barely visible when you switch the switch, but if you look REAL closely – you can see them – they’re little round lumps that a wiper assembly rubs over.

This – I hoped – would clear up the dead spot, butt the switch itself was still stiff to operate.

I looked some more, and found that there are two tiny ball-bearings that are prolly spring loaded, which move in/out of several holes and a slot. These provide the detent for hi/lo, and the spring loaded return for the hi-beam flash function.

I tried spritzing (tech-term) some WD-40 on these – with little effect. So I got out my moly-lube (left over from spline stuff), and poked some into the holes with a toothpick as I operated the switch back and forth.

I also lubricated the contact area with a non-greasy lubricant (LPS) made for this sort of application (at least it sez so on the can).

Much smoother now.

Reassembly went OK, until I started looking for the brass piece for the horn button (which I found in a rag I used to protect the tank), and until the tiny – special – screw holding the horn button went flying. Finally found a replacement for it down in my cellar junk-screw-bin. (It is a VERY special screw – don’t lose it!).

Turned the ignition on and found:

  1. No dead spot
  2. Regular (55/60) headlight bulb appeared brighter than the 80/100 had
  3. Much smoother operation
  4. Horn blowing continuously – had the brass thingie in backwards.


The interior of the switch had obvious road-dirt in it – the bike is 12-13 years old, has obviously been in the rain (rain trails inside the switch), butt – the contacts, once cleaned looked FINE, and all wiring was fine (no solder melting).

I seem to remember some other prez’s dissecting their failed switches and finding that the soldered connections to the contacts had failed, indicating to me that there was an AWFUL lotta heat – prolly caused by dirty contacts (resistance) heating up enough to melt the solder. The accumulation of road-dirt could cause this sort of high-resistance failure. The switch is NOT well weather sealed (surprise!), and there is no obvious way to seal it – but a seal where on the joint on the top where it attaches to the handgrip would help a LOT (gonna use some sealant on this – real soon now), since most of the rain marks looked like they came down from this joint.

My advice – don’t do this in the driveway – and I’ll prolly do it on a semi-annual basis. A trick I learned when rebuilding sailboat winches is to do this sorta thing inside a shoebox – the parts then only have one way to jump out (up) so the chances of retaining all of them is much higher – gonna do it this way next time. If you are seeing what appears to be (a) less light out front (b) stiff or notchy operation (c) a dead spot – you MAY be able to rescue your switch before total failure occurs. If not – you need a new one anyway, so nothing ventured nothing gained.

If any prez’s have dead switches laying around – I’d be interested in dissecting a few to see what failure modes I find, or hearing from people who have opened up the failed switches. Plus – if you send it to me, I’ll have spares for all those little screws/balls/springs that tend to go flying. EMail me for my address if you’d like to donate dead switches to the cause. I’ll summarize what I find and post it.

Headlight Switch Repair – Addendum

By Leo Horishny
September 1998

I’d like to expand on Don Eilenberger’s helpful dissection of the K bike headlight switch. My story looks like I’m heading towards a switch replacement, but after my light wiggled off last night coming home, I was prompted to follow his instructions and take my switch apart hoping I could clean and repair my switch.

2 prep items I added to his, I laid a couple of large light colored towels on the ground under the area to highlight and capture any rogue parts that I might miss, and I used a couple of largish floppy magnets to hold my screws in roughly the same pattern as they came out of the switch. Including the spring that rests on top of the horn button screw and is between the handlebar and the switch. I didn’t have a brass piece he describes with THIS outer spring, HOWEVER, when you take the button off the switch, there is another spring inside the button itself and in THAT spring there’s an infamous brass thingy. As you unscrew the horn button from the switch, you should be able to allow the button to fall into your palm, with the spring and the brass piece staying put in their stem.

I can attest and aver that the horn will sound if you forget to replace the spring that rests atop the horn button securing screw between the handlebar and the switch casing when you screw the switch back onto the handlebar!

When you get to the light switch itself be aware: There will be 3 springs to control when you take the switch out of its housing. 2 are on the right side of the switch (with switch oriented as it’s supposed to sit) and 1 is on the left side. The ones on the right are behind the brass contacts for the lights, the one on the left is behind the upper ball bearing pivot Don describes. BE CAREFUL as you remove the pivot the switch button rotates on; as you take the pivot out, look and plan where you’re going to place your fingers to secure the springs as you re- move the switch.

As he describes, Your Outcome May Vary as to whether this will cure your woes, but it was a pretty straightforward operation using reasonable caution.

Headlight Switch Repair – Addendum II

By: Chris Bell
October 1999

I just did a headlight hi/lo switch repair using Don E’s repair FAQ (above). After conversing with him about some discoveries, he suggested submitting this to supplement the original FAQ.

Ideally this job would be done after removing the gas tank and unplugging the entire switch from the wiring harness so it could be cleaned and repaired on a suitable table. However it can be done as Don and I did ours, with the plug end of the switch still connected somewhere underneath the gas tank. I used a magnetic bowl purchased at a tool store to hold most of the parts and laid a light colored bath towel across the tank and inside the fairing to catch anything I dropped. (WARNING: somehow secure the towel or do this in the garage or else a breeze can send all these important little pieces flying!)

My switch was dirty but that was not the only problem. When the problem originally surfaced, my low beam worked but not the high. When I started working on it Saturday everything had reversed, the high beam would work but the low beam had now failed. It turns out one of the solder contact “blobs” in the switch broke off and was rattling around inside the switch at first allowing the low beam to work, and later the high beam only.

After cleaning, I was able to attach a new “blob” of solder in place of the old one so the light is functioning fine now. I went to the BMW shop and ordered a replacement switch for $69 which will ensure that my repair will last FOREVER. (Law of Spare Parts – if you have replacement parts handy, you will never need them).

Here are some additions to President Eilenberger’s repair instructions:

  1. For cleaning, the switch can easily be taken apart further than Don explained in the FAQ. Once the switch is disassembled as far as described, the hinge pin that holds the hi/lo rocker can easily be pushed out with a very small screwdriver or nail. The button part and the *many* springs, pins and contact plates in it can then be fully removed from the switch “frame” that still has all the wires soldered to it. This allows full access for cleaning all the little parts and contacts. Separate the rocker button from the frame slowly so you can identify where all the parts go during re-assembly. (It is possible to hold all the parts in place with your fingers during the separation.)
  2. The detent “ball-bearings” that can be lubed with a toothpick and grease are in fact spring loaded pins similar to the “funny brass” thingie that goes in the horn button. They can be cleaned and lubed after disassembly.
  3. Access to the screw that holds the horn button in place is buried deep in the back of the whole switch assembly. You can get a straighter shot at that screw with your screwdriver if you depress and hold the horn button while undoing and replacing the screw.
  4. The brass thingie that causes the horn to operate continuously if installed improperly: I would describe it as a pin with a collar located not quite in the middle. The shorter end of the pin goes into the spring that goes into the hole on the back of the horn button. The longer end of the pin goes into the “guts” of the switch.

As I said, after complete disassembly, I was able to heat the connection that had crumbled in my switch with a soldering iron and reconstruct the failed contact. When finished, I cleaned everything thoroughly with contact cleaner and re-assembled the switch. Before I installed it, I doused the insides and back of the whole thing pretty good with an aerosol silicone spray that will act as a lube and protect the contacts from corrosion too.

Good Luck!

Headlight Switch Repair – Addendum III

By Paul C
July 2005

8-2004 Problem: Headlight switch very hard to move and dead spot where light goes off. Miles: 45,000. I live in a place where it never rains. Even though the switch is carefully enclosed, I think dust and dirt gets into it as you drive. I was surprised by the build up of dirt I found in my switch.

Thanks to the directions I followed from Don Eilenberger (above).

If you could buy this switch for $30 I would recommend it. My switch works well but it still has a flat spot. In the day it is not possible while riding to know for sure if my head light is on. Hopefully, I won’t need to touch it for many years. It has been over a week now and the switch is working well.

Items needed:
Large clear plastic bag. Dielectric grease. Q-tips & hand cleaner or other light degreaser. Do not use strong solvents or brake cleaner. It will destroy the plastic. #2 phillips screwdriver. Very small straight screw driver to pry. Toilet paper or shop towels to clean in small places.

TIME:  ~ 1 – 2 hours.

Do not push or play around with the switch unnecessarily until full disassembly. The key part is the headlight button. Once removed the switch can be rotated up (see picture 4) even with the pin in place and the springs will shoot out!

The dealer quoted me $65 + tax for the switch. You should call your dealer first for price and availability. If you make a mistake and springs go flying you will need to buy a new switch – so get ready in advance.


  1. Remove screw (one) and pry Headlight Switch off the handle bars.
  2. Remove 6 screws (note where different lengths go). Try to keep each screw where it belongs in the piece it holds down, where possible. Unscrew Signal button screw.
  3. Separate the inner switch from outer cover – use a very small screwdriver and flex the outer cover. It will also take some effort on reassembly – a little silicone or grease could ease reassembly.
  4. Remove the screw for the Headlight Button Screw (#8). WARNING: At this point if the switch is pushed / rotated it will swivel to a position where the springs and other parts will POP OUT!!! Take a small pointed object and push the main pin out. It should go in and out easily.
  5. Cover entire switch with clear plastic bag and slowly rotate switch out. Keep pressure on the U-shaped parts that the springs push against to prevents to parts from popping out. There are two U-shaped parts towards front of the bike and one round thick bullet shaped pin with a spring inside it facing the back of the bike.

Re-install all parts – keep covered with the bag until the headlight button is screwed in. Then you are safe from the springs popping. TAKE YOUR TIME AND DON’T RUSH.

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