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.

Connectors:

While you are shopping for wire, check out the supply of connectors. For the large 6 or 8 gage wire, you will find heavy battery terminal type connectors. For 10 and 12 gage wire, female or bolt style connectors are easy to find. Since you want to crimp and solder all electrical connectors, the plastic covered ones are a pain to use. Instead, I buy regular uncovered connectors and slip a piece of heavy shrink tubing over the wire before I attach the connector. After crimping and soldering the connector on the wire, I slide the shrink tubing over the bare connector and shrink it to a nice tight fit that covers and insulates the end of the wire.
Note: The best female wire connectors that I have found were stainless steel (very corrosion resistant), high temperature resistant (heat causes connectors to open and loose the tight connection) female connectors for $.17 each at Ace Hardware stores.

Where to Start?:

I always start at the battery and work my way forward. Since there are several wiring variations with the same basic scheme, I won’t go into individual model details. On my R90,R100S and R100RMS and others, the wiring was simple to upgrade and in all cases provided a noticeable improvement in the bike’s performance. Charging was improved, lights much brighter and steady, voltmeter pegged at 13.8 volts (even the BMW Motometer volt meter quit jumping around), starting easier and mileage improved to 78 MPG … just kidding. But seriously, the time and effort it takes to clean all the old connectors is about the same time you need to upgrade the wiring, and besides, you never really get the connectors clean 100% and they have been heated so many times that many have lost their ability to grip the male spade and provide good solid contact.

Impact on Headlight Output:

Remember that your halogen headlight produces 100% of their design luminous output at 13.5 volts. When your operating voltage drops to 95%, or 12.82 volts, your headlight bulbs only produce 83% of their rated light output; at 90% or 12.15 volts the lighting output is only 67% of what it should be and when you hit 85% or 11.47 volts, your headlights are only producing a lousy 53% of their rated output. What makes this observation more interesting is the fact that many riders install higher wattage bulbs in the belief that they will get better illumination … Not! Depending on your electrical system and how well it is delivering power to the headlight, you can actually end up with the same, slightly more or even less illumination than with the standard headlight bulb that was replaced. If you would like to read more on electrical systems and headlight upgrades see Dan Stern’s excellent articles at: lighting.mbz.org/tech/how_to/relays and lighting.mbz.org/tech/info/blue_bulbs and lighting.mbz.org/tech/info/superwhites and probably the best at lighting.mbz.org/faq

Why Use Larger Wire?:

So why use larger wire? Because larger wire greatly reduces the resistance (and therefore heat generated) that your old charging system has to overcome by working harder and producing less output. The smaller stock wire was fine when your bike was new and had nice shinny and clean connections and new alternator brushes and rotor. But things have changed and your alternator and charging system are a bit worn and any help you can provide will result in better charging and reduced heat under the front engine cover.

Replace/Add-On Negative Cables and Wires:

Start at the battery and start with the simplest upgrade. The ground cable. Yes, the ground is just as important as the positive wire feeds on your bike. Why BMW choose to mount the battery ground cable to the hollow transmission bolt is beyond me, because if you strip the bolt with repeated removal, you strip the transmission case! Not a pretty picture.

I fabricate a 6 or 8 gage cable with a heavy battery end on one end and an open “C” connector on the other. I then measure the distance from the battery (-) post to the right rear coil bracket mounting bolt, cut crimp and solder the wire and that’s it. On some bikes I have eliminated the transmission (-) cable because it is a problem waiting to happen, but in most cases I simply leave the two (-) cables attached – one to the engine(stock) and one to the frame (add-on). Cost: $.75. Time: 15 minutes. Difficulty: 1/2 wrench.

While you are making (-) upgrades, check under the top engine cover and see if any PO has added the extra ground wire from the starter mounting bolt to the inside of the front engine cover. If not, it’s time to add one. Kari Prager of California BMW wrote a great article on R-bike charging systems that explains why the addition of this extra wire is a good idea, especially those R-bikes with the electrostatic painted front engine cover. Kari’s article can be found at: www.ibmwr.org/tech/rtech/charging.info.html . Keep in mind that this extra ground is also a good idea for older R-bikes when you consider the fact that a gasket and some built up corrosion on the bolts separates the engine block from the timing chain cover. For this upgrade, I normally use a 10 gage wire with small bolt connections on each end – one that mounts under the starter mounting bolt head and the other to the front timing chain cover. Some recommend that it go to the diode board mounting bolt, but anywhere on the timing chain cover inside the front engine cover will do just fine.

The Positive Side of Things:

Now for the fun part … the positive side upgrades. Look and see what you have and where it goes. Then decide if you want to replace the existing wire or run an additional wire to the same destination. Sometimes this is not always possible. For example, a (+) wire running from the battery to the starter relay has only one male spade to connect to. In that case, I normally replace the stock wire with a new heavier wire.

Note: Some bikes have a (+) wire running from the battery to the starter relay under the tank and others have the (+) wire running from the battery to the headlight shell fuse board and back to a relay. Makes no difference. Just replace as you go and everything will start to improve before your very eyes. Keep working your way forward replacing wires as you have time to do so. Nothing bad will happen if you only upgrade a wire at a time, but you do want to work from the battery to the final points of use. Just follow existing wire paths to keep things simple or run the wire however YOU want them. This isn’t rocket science and you can be as creative as you want – just remember the shorter the length of wire the less resistance and heat it produces. If you can find a shorter route, go for it!!!

Inside the Headlight Shell:

Once you get inside the headlight shell, things really start to get fun and where flexible wire becomes important. Look at the red section on the lower right side of your fuseboard. You will see (+) feed wires coming in and (+) feed wires going out. The ones that are good candidates for upgrading are:

1. (+) wire from battery to fuse board
2. (+) wire from fuse board to ignition switch
3. (+) wire from fuse board and ignition switch to headlight relay
4. all wires connected to headlight including the ground wire

All of these are female/female connectors and 10 gage wire works wonders. Your ignition switch power and headlight relay now have great power and can feed it out throughout the system. One thing to be careful of inside the headlight shell is getting too much wire or too stiff a wire inside that can contact the hot surface of the headlight reflector. Since stock wires are smaller, they are easier to compact away from the reflector. This isn’t a big problem, just a situation that you should be aware of when connecting and routing the new, larger wires. For more inf. see lighting.mbz.org/tech/how_to/relays page 5 of 7.

Upgrade Without Replacing Stock Wires – Replace the Connectors:

For those of you that don’t want to run heavier wire and still want an upgrade to your electrical system, I suggest that you consider replacing the female connectors with new, high temp stainless steel ones. I have tried forever to clean the inside of female connectors and you know what? They are never clean. If you don’t believe me, clean a corroded female connector as best you can with whatever tools and products available. Then, remove the plastic cover that BMW uses and look at the connector … old, crusty, tarnished and warped from repeated use and connect/disconnect. Just cut off the old connector, slide a piece of good heavy shrink tubing down the wire, attach and crimp the connector on, solder, slide shrink tubing over connector heat shrink and you are done!

If you replace most of the connectors in your wiring circuit, you will notice a distinct improvement in your charging system.

Soldering Tips:

Only use rosin core and NOT acid core solder. 40/60 or 60/40 solder works equally well but the thinner the solder, the easier it melts, which is what you want when applying the solder. Available at any hardware or auto store.

Replace Relays:

You don’t need to spend your entire allowance when buying relays to replace those old moldy ones you have hiding under your tank. Relays are relays are relays … and the world has more Bosch relays running vehicles than all other brands put together. There are many different manufactures that make replacement relays for the Bosch unit. Look in auto stores or better yet a local automotive electrical shop. New relays are available for as little as $2.75. I know because that’s what I buy them for at an Ace Electrical outlet here in town.

Note: All relay connections are coded consistently using a universal numbering system (just like all bearings which is another replacement part you can buy from any bearing retailer). Here’s the codes:

• 86 is the relay switching (control) circuit input, or wire from the button or switch
• 85 is the relay switching (control) circuit output, or “ground”
• 30 is the power circuit input, or “hot” (+) feed to the relay
• 87 is the power circuit output, or the output that activates the unit (i.e. horn)

Some relays have more than one “87” terminal which you can use to power two different items. Be careful though because “87a” terminals are not the same as an “87” terminal. If you have a relay with an 87a and 87b, the 87a unit is always “on” until you hit the control button or switch, in which case it shuts off. The 87b unit (i.e. horn) is “off” until you press the button or switch when it then turns “on”. For more inf. see lighting.mbz.org/tech/how_to/relays page 3 of 7 and 4 of 7.

That’s about all there is to accomplishing an easy, low-cost upgrade to your bikes wiring system.

Roy Truelsen #4363
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Comments:
There are quite a number of things I do not like about what Roy Truelsen said in the above article.  There are also some serious errors.    If you really need new wiring, I suggest an all new wiring loom, either from BMW, or the aftermarket, or, just fix the one or two wires with problems.  Increasing the gauge of the wires will not do what he said about the charging nor the light output from the headlight, unless the wire connections, switch, etc., are in terrible condition.    Eastern Beaver Company makes entire plug and play kits to improve the headlight output, using small relays, if that is what you wish to do.  There is a moderate improvement only. You can measure the voltage at the battery terminals, engine off, lights on, and compare to the voltage at the headlight socket, up to 0.7 volt drop is OK.  The charging voltage, measured AT the battery terminals, is best to be ~14.2, so adjust the voltage regulator after all the wiring connections are clean, tight, etc. Keep in mind that anything you do to the electrical system must be safety-considered, and needs to be at least as reliable as the original wiring was when BMW manufactured the motorcycle.  Rather than take on every single complaint I have about the article, above, I will make two additional comments:

#1.  NOTHING drives a shop technician or a good home mechanic crazier than to see non-standard wire color coding.   You are UNlikely to find the correct colors with correct stripes, at your nearest store, whether marine or hardware store.  Metric color coded wires are not easily found.

#2.  https://bmwmotorcycletech.info/wires&codes.htm contains a large amount of information on wire colors, American sizes versus metric sizes, what the colors mean, etc.
Snowbum