Hello Wolfgang, i have to ask why?  BMW airhead wiring systems are very reliable in all my years of being around them I have never seen an incident where a main fuse is needed.  The sort of short that causes major damage is usually when someone forgets to disconnect the ground when opening up the front cover and shorts out the diode board positive connector.  

I would say if you do install a fuse it can't hurt but just means extra work that I don't think needs to be done and adds just one more fuse to pop at an inconvenient time, LOL.  Anyway why use a fuse, how about a circuit breaker?  

I have a lot of miles and years on my main riding bike and have never had anymore than the 8 amp fuses pop in the headlight bucket and those shorts were my own fault or due to years of riding in all kinds of weather causing the issue, not due to the bike's design.  St.

A main fuse was a rather standard "upgrade" for US owners back in the 1970's. I've owned several US-version R100's over the years that had this mod added. It does sound like a very good upgrade, but like Steve said, after thousands of miles I've never seen that fuse blow. That is to say... actually protect anything. Let me go though all the details, and then you can decide.

• 1. If you want to add a "main fuse", then the place to add it is to the RED wire taking power off the battery. This is because the power that could possibly hurt any other component is in the BATTERY. Snip back the BMW harness ring lug terminal on the red 14ga wire at the battery + terminal. Solder in a weatherproof "flat pack" fuse holder. (As shown below.) Apply at least 1 layer of heat shrink insulation over the solder joint. Solder a 1/4" ring lug to the other end of the fuse holder and again add heat shrink insulation over the tubular portion. Then install a 20A or 25A fuse at that position.

► Shown above is a weatherproof flat pack fuse holder, typically available at your LAPS. The one with red wire comes with 16ga wire. For the current carrying capability of a "main fuse", you want to use the nearly identical version with the larger 14ga yellow wire.

That's a lot of work for no benefit. Especially if you don't have soldering skills or a heat gun and heat shrink tubing.

• 2. If you really want to upgrade your harness protection, then the only unprotected place is the clock on the S and RT versions. The clock is powered 24/7 and the only component without a fuse. I suggest you use a weatherproof flat pack fuse holder with red wire. Solder on 1 male and 1 female spade terminal to the ends, and then (sort of like adding an extension cord), insert that between the fairing harness and the terminal on the rear of the clock. Then add a 1A fuse to the holder.

• 3. If you really want to upgrade your harness reliability, then you can replace both OEM pointy-end fuse in the headlamp shell with modern flat pack versions. The older, spring-loaded variety fuses haven't been used for anything in 30 years exactly because they are so unreliable. Besides that, older style replacement fuses are almost impossible to find when you're 100 miles from home. 

To make this conversion, buy 2 accessory flat pack fuse holders... which look like this...

Solder on insulated spade terminals to each wire end. Remove the old OEM fuses and reconnect the 2 sides of the circuit by electrically connecting the new style fuse holders. Add a 7A flat pack fuse to to each new holder. 

► On a 1978 bike like yours with the fuses inside the headlamp shell, this connection is made by connecting the Green terminals to Green/Black. And likewise, the Gray terminals to the Gray/Black. You can clearly see the right-to-left electrical flow pattern when you look at the multi-color circuit board without all the wires blocking the view.

► On a later model single-sided machine you would remove the entire plastic fuse block and plug the new fuse holders directly into the terminal pairs already on the harness.

And of course, since all these terminals are out in the weather, we would treat them with anti-oxidation compound.  

Hope this helps.

So again, I write, for this application why not go with a circuit breaker?   

A boating supply store will have a variety of circuit breakers in the amperage range you most likely will choose to do the job and they require the same skill to install.    St. 

Thank you all for the sage advice. Will probably change to the new style fuses. I can get the old style, but the quality is shite.

The 8 amp traditional style fuses are available from Bussman company on Amazon for reasonable price per package and are far superior than most found in auto parts stores, unless you have a very well stocked auto store.   

Yeah, I bought a couple of fuses a long while back from a BMW dealer and they were pretty bad.   Not to be a pain in the butt but, I butt heads with a lot of people on fuse issues.   I see no problem with the stock fuse system and I say that because I have had very good luck with it over years of riding in all kinds of weather.    The only times I have problems with blown fuses is right after I do any overhaul on my bike and am reinstalling turn signals or adding lights.  I may blow a fuse or two until I get things sorted out with the wiring but after that I never have a problem, at least not enough of a problem to force me to make changes to sufficient in my mind wiring that is in place.

Then again, some people have to improve, it is your bike.   Good luck.  St.

Then again, some people have to improve...

Yes, the old style fuses are still available, but IMHO you're not looking at the "big picture". 

• To begin with these pointy-end fuses are totally dependent upon a very small spring pressure to overcome surface resistance and make good electrical contact. The design was barely passible in 1950, and you'll notice that they haven't been used in ANY new car or motorcycle production in 3 decades. It's because the automotive industry as a whole judges them inferior.

• Yes, the newer Bussman versions are better simply because the end cap metal doesn't promote corrosion like the OEM Bosch did back in the day. But most people today ride motorcycles for enjoyment, not to test their repair skills on the side of the road. So it's not about "what can be made to work", instead it's about reliability and completing your 600 mile ride to the National or your "one day out with the guys" without mishap. And we're not discussing the pros and cons of a $450 alternator, we're talking about a handful of fuses and fuses holders totaling $25.

• And why is it that ultimate electrical reliability is so important ? Consider that a lot of your typical circa 1978 model bikes originally came with points ignitions. If you have an intermittent electrical connection (say 1 millisecond), then the points ignition may miss 1 ignition firing in 2-3000. The engine continues to run and the rider wouldn't even be aware of this situation. But if you convert that same motorcycle to an electronic ignition, then it's a whole different story. One millisecond of electrical connectivity means the EI software has to reboot. The ignition may miss 50-100 ignition firings in 2-3000. The engine stumbles and misfires. The effect is very much felt in the seat and rider controls, and the rider is acutely aware that something isn't right, and turns to head for home. The rider's trust in his bike's reliability is shattered. Fun gone; ride time lost.

In short... you can get away with a lot of dodgy connections when your electrical system is purely analog. But when you start introducing transistorized and digital components, then you've really got to clean up your act.

Richard, considering the electronic ignition system on my bike is NOT fused, it makes no sense to change the fuse system to improve its operation.   This lies within the realm of keeping up with maintenance on the bike with as you are so quick to point out means occasionally cleaning contact points of corrosion.   

No fuse in the ignition system, so what is the point of changing the fuse system?  Not even the headlight is fused on most /6 and newer bikes.

Let's keep it apples to apples, changing the two fuses from inside the headlight shell is NOT going to improve performance or reliability of the ignition, starter, or headlight systems.    St.

Of course if a main fuse is added as is being discussed here, I fully agree the old style fuse system is inadequate.  At this point poor contact could cause issues with the tree systems I point out.  At this point if I was foolish enough to add a main fuse, I would add a good circuit breaker.   

For the taillights and turn signals, the old system works just fine.  St.

How many fuses are in modern airplanes these days?  St.

Posted by: @14724

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No fuse in the ignition system, so what is the point of changing the fuse system?  Not even the headlight is fused on most /6 and newer bikes.

Point taken.