Wiring Color Codes

This covers most of the basic wire colors used on Airheads.  As the electronics got more complex, more combinations came into play so it’s possible a few of the more obscure ones may see other uses.  Always double check factory wiring diagrams, and yes, even they can have a mistake or two.  PowerBoxer.de has a copy of the Haynes ones. And here’s a link for more about Airhead relays and terminal designations.

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Panasonic Battery Upgrade

Maybe I worry too much, but I always imagine the worst when the GS tips over onto a cylinder head and the electrolyte in the battery starts sloshing around. The vent tube is routed low enough so that any acid that does manage to escape should make it to the ground without splashing on anything metal, but there’s always the chance that won’t go according to plan. And regular maintenance of the electrolyte level is also necessary to keep the battery in good shape. That’s not a big deal, since removing the battery is pretty easy on the GS. But it’s just one more thing to screw around with, and there are ways of keeping things simple when it comes to batteries. Frankly I was surprised when I checked the log for the R100GS and found that the BMW battery was almost six years old, as it had given no signs of ageing like slow cranking or unexpectedly going flat. But six years is plenty for any battery, and I’d just as soon replace it in the comfort of my own garage than have to bump start the bike somewhere out on the road until I can find something that would fit. I’d had pretty good luck with a Panasonic sealed battery in the K1200RS, and with Digi-Key’s $58 and change price (including shipping), swapping out the wet cell BMW battery for the maintenance free Panasonic was a no brainer. A week after the check went in the mail to Digi-Key, the Panasonic was sitting on the door step.

As shown by the part number on the side of the box, the correct battery for the R100GS is an LC-X1228P, the P referring to the terminal type. We want flat lugs with bolt holes, ideally with positive and negative positioned just like the OEM battery, and that’s what we get with this Panasonic. They call it a VRLA battery, short for valve-regulated lead-acid, and it uses AGM (Absorbed Glass Mat) technology to eliminate the liquid electrolyte. The LC-X1228P is rated at 28 Amp Hours, just like the original. This battery came with a few California specific stickers adhering to the top surface, each of which left a nasty bit of paper and glue behind when I removed them. A little 3M feathering disk adhesive remover took care of the problem, but it also removed some of the printing from the top of the battery and left a hazy surface in place of the shine every where else. Size wise, the Panasonic is about 5/8″ short in the long dimension, and about a half inch taller when measured over the terminals.

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R100GS Euro Headlight Switch Upgrade

Is it just me, or is there something un-American about not being able to turn off the headlight on your motorcycle? Especially on a dual-sport bike that spends a significant amount of time donking along at low speeds off road where the factory alternator can’t keep pace with ignition system and headlight drain. Ironically, there is a solution to this problem in the form of a factory BMW part used on bikes destined for delivery every place but America.

As shown in the photo at left, the BMW part number is 61 31 2 305 232, and the cost is somewhere around $75. That’s a ridiculous price for such a simple device, but when you compare the cost to that charged for an equivalent K-bike switch it’s a screamin’ bargain. Your friendly dealer may have to scratch around a bit in the European versions of his parts catalog to locate it, but larger dealerships should be familiar with where to look as it’s a fairly popular upgrade. Even better, it’s also one of the easiest to install, so let’s get started.

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R100GS 4 Way Flasher Upgrade

Lately it seems I’ve been spending a fair amount of time at the side of the road, either at crash sites or just stopping to look at a map. In these situations visibility is a good thing, and the K bikes I’ve owned all had 4 way flashers as standard equipment. The GS is wired for them, but the bits to make ’em work aren’t always all there. That’s easily remedied with a call to Sam at Re-Psycle BMW Parts, a purveyor of new & used parts located back in my old stomping grounds of Lithopolis, Ohio. Your friendly neighborhood dealer should also be able to get them, but if you’re going to have to wait for him to order them anyway, why pay full boat when you can get ’em used for half the price?

Here’s what you’ll need:

61 31 1 459 224 – 4 Way Flasher Relay, $55.00
61 31 1 244 708 – Hazard Switch, $13.50
61 31 1 244 709 – Symbol, Hazard Switch – Included

Keep in mind that the prices quoted above are for used parts, and might vary depending on the condition of what Sam has on hand and how polite you are when you talk to him. In my experience, Sam’s not real good at answering email, so it’s best to call on the phone. His service is great, though, as I had the parts in hand in less than a week, not bad seeing as I’m now sited in California.

You should also check the part number on the flasher relay that comes on your bike. I understand that the later GSs come with a 4 way capable relay (below, left) already installed, and it should have a number on it that encompasses the last seven digits listed above. The relay on my 1993 (below, right) had the digits 2 306 014, and would not engage the 4 way flasher function. Also note that the 4 way flasher relay is also standard equipment on all K75, K100, and K1100 bikes, and that info might help Sam get you the correct part.

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Headlight Switches & Headlight Relays

This article was originally written (and since then, expanded/edited numerous times) because someone asked about the left-hand switch of BMW Airhead motorcycles if using higher powered headlight bulbs. He did not understand why the existing stock headlight relay would not automatically eliminate wear on the switchgear. The simplified reason is that the stock headlight relay does not do what many think it does, at least on most, especially later, Airhead models. Variances of his question have come up many times, often on the Airheads LIST, but also on various other forums, and even for other BMW models.

It is important to know that the main purpose of the stock headlight relay FROM 1978 is to turn off the headlight, leaving the dash lights and rear running lamp on, during the time the starter motor is cranking the engine. The relay turns off the headlight during cranking, and that’s all.The stock headlight relay from 1978 also does not  do theswitching between high & low beams.  NOTE that the high beam flasher (‘passing lamp’) function remains, due to a green wire from the ignition switch, as a separate circuit. The headlight relay may or may not turn off the headlight, during engine cranking, depending on year, model, & country shipped-to. On some Airheads, the high beam flasher button (‘passing lamp’ function) MAY be available with the ignition off. It is a matter of where the green-colored wire goes to. It is easy to move a green wire at the ignition switch, and thereby have the ignition be ON, but the headlight OFF, in the PARK function, but there is more to this, and this is not the point of this article.   

Using additional relays to control higher-powered headlamps (stock is 55/60 watt) is a must; although some have gotten away with not doing so for some time. Note that the left bars switch assembly is fairly expensive. It is not designed to handle high-powered headlamps, and it would have been, …perhaps, …better if a relay had been used by BMW to handle all the current flow to the low and high beams. This is not difficult to accomplish, and such as the Eastern Beaver kit does it. With that kit installed (or, your own two relays), the bars light switch(s) would only pass current to the extra relay’s COILS. This means that using accessory relays will reduce wear on the left switchgear even with the stock headlight; and usually will increase light output slightly due to a more direct current path from the battery to the relay.  This increases the headlight voltage to closer to battery voltage….another way of saying this is that a more direct power path reduces wire and some switching losses.

Sources for appropriate relays are any auto-parts store. However, www.EasternBeaver.com sells complete plug and play kits for your motorcycle, and they may even still have a version with a modulator if you wanted that.

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Basic Electricity 101+

The below article was written to furnish THREE types of information:

(1) CONSIDERABLE amount of BASIC & SLIGHTLY ADVANCED INFORMATION on electricity & Airhead problems. The approach used here is probably different than in most manuals & troubleshooting guides. Although some hints are given in this article on some common faults, this article should be used in conjunction with my other articles, particularly: http://bmwmotorcycletech.info/electricalhints.htm

(2) Common problem areas, explanations of some of the circuitry. A discussion of such as batteries; starter motors, voltage regulators, etc. Other articles will get far deeper into these things.

(3) An addendum that may discuss particular points that has come up, or some topic of interest. Some is at the very end of this article.

Available to you are certain helpful booklets from such as Motorrad Elektrik, Chitech, Haynes and/or Clymers manuals (and, perhaps, a schematic in the rear of your owners booklet or on the Snowbum website).  In my opinion the Chitech electrics manual and the owners book or factory schematic, or schematics on the Snowbum website (and some elsewhere’s, and I have links to these on the Snowbum website), are THE BEST sources for electrical information for the Airheads.

I recommend you at least purchase at the Chitech Electrics Manual. The Chitech (Chicago Region BMW Owners Assoc.) BMW Electric School Manual is THE BEST manual for BMW electrics, from basics to full-blown technical details, components, diagrams, etc., & includes the singles & all Airheads; even some on the /2 era. It is VERY complete. Only a few errors, for which i wrote an article/Critique:  http://bmwmotorcycletech.info/chitechelmnl.htm

See http://bmwmotorcycletech.info/url.htm  for more information on Chitech, and how to order their publication. Some of the total-bike schematics are not reproduced well, that is the only substantial problem with that manual. Get the manual anyway.

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Odyssey Battery Upgrade

It’s a long story, but a while back I ended up with an extra Odyssey PC680 battery, and I thought it would make a nice upgrade for the R100RT. The bike came to me with a Wesco AGM battery of indeterminate age, and it was a monster. It also used the steel hoop type hold down that has a pair of spokes on either side. The Odyssey is much narrower than the Wesco, and the spokes were too long to hold the Odyssey firmly in place.

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Auxiliary Electrical Bus

The R100RT doesn’t use the modern CANBUS electrical architecture of the latest BMW motorcycles, and in my book that’s a good thing. As a result there’s no need to play games trying to trick computers into providing electrical power for accessories, but the flexibility and safety provided by a well designed and built auxiliary electrical bus pays big dividends even on a twenty year old bike. I plan on powering an electric jacket, electrified tankbag, GPS, and auxiliary lights, and didn’t want a hodgepodge of wires running around under the tank. I used a Centech AP2 fuse panel when I added driving lights on the R100GS, so decided to go that route with the RT as well. The AP2 is an upgrade to the AP1 on the GS, and it has two banks of fuses and power taps, each with a separate power source. That would let me wire one so that it was always on, and switch the other bank with the ignition. That’s a nice option for a GPS, which doesn’t draw a lot of current and is sometimes used when the engine is off. Yet there’s no chance of leaving on heavy drawing items like a jacket or lights if you forget to turn them off, as turning off the ignition will kill them all.

The biggest problem was

finding a place to mount the AP2. Even though it’s not very big, the spot under the seat I used on the GS was taken up by the BMW fuse box on the RT. After sleeping on it a couple of nights, I came up with the idea of fabricating an aluminum plate that would fit under the left side cover, and mounting the components on it. That location is close to the battery, and as it turns out, close to trigger signal sources that will be used with ignition and high beam sensing relays. I toyed with the idea of mounting the plate with hose clamps, but didn’t like the damage that would result to the frame tube paint. Instead I used a combination of heavy duty zip ties and industrial double faced tape.

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Electrical Wire Upgrade

To help the voltage regulator and the entire charging system, an easy and inexpensive upgrade is to replace old, small, worn and sometimes corroded stock BMW wires with a set of upgraded heavier wires you make yourself. Here’s how:

The Best Wire to Use

For the best wire, go to a marine supply store and look at their selection of bulk wire. They will have wire as thin as 22 gage and as thick as 6 gage, with costs ranging from $.11 to $.49 per foot. The marine wire is rated for 600 volts, is oil-water-gasoline resistant, and is made with very fine multiple strand wire. The finer the wire used in the multi-strand wire, the more flexible the wire will be to handle and install, which is important when working within the tight confines of a motorcycle.

If you can’t find a marine supply store, auto parts and hardware stores also carry quality multi-strand wire at reasonable prices. I have used this material in the past and it works well but is not as flexible as the marine grade wire.

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