R1100S Auxiliary Fuse box

Installing an Auxiliary fuse box on a 2004 BMW R1100SA

This information is provided “as-is” and free of charge. The author assumes no liability for incorrect design, construction, or assembly. I was able to perform this modification to my bike, I do not know if it will be possible for you to perform the modifications to your bike. I believe this information is correct and complete to the best of my abilities. When in doubt, consult a professional mechanic.

Many thanks to Brian Curry for proof-reading!

Note. I put the text that describes the photos above the photo.Background: I have added a few electrical accessories and I’m planning on adding more. I have Gerbing heated clothing and I added PIAA 1100X driving lights with an Autoswitch.

Both the Gerbing and PIAA’s are wired directly to the battery (the PIAA’s are controlled by a relay). This has a couple of implications.

  1. There is a rat’s nest of wires tucked in behind the battery.
  2. The wiring harnesses for both include fuses; however, the fuse is located very near the battery terminal. This requires removal of the fairing to access the fuses. While I have not yet blown a fuse, it would be highly undesirable to be removing the fairing on the side of the road in order to deal with the problem.

Addition of other accessories will only further compound the problem. Here’s a shot of the mess behind that was behind the battery.

Now, I could have cleaned this up without installing the fuse box, but it still does not solve access to the fuses without removing the fairing, nor does it make adding other accessories any easier.

Proposed solution:

Add an auxiliary fuse block behind the fairing. I chose a Centech AP-1, pictured below.

In my opinion, selection of the proper wire size and type is critical. First, some simple load calculations:

Gerbing: According to their site, my jacket liner and gloves constitute 99 watts. If assume a nominal battery voltage of 12 volts (not very realistic, it’s normally well over 13 volts), that means I need to deliver 8.25A (i = p/e). I have been told that 99W is not an accurate value and it is actually higher. If I assume it’s 120W and a nominal 13.8V battery voltage, it still gives me around 8.6A. I’m comfortable with 8.5A.

PIAA: I have two 1100x driving lights @ 55W each. 110W/12V gives me 9.2A. If I assume 13.8V, it get ~8A.

Gerbing + PIAA = 8.5A + 9.2A or 17.7A.

12 Gauge wire is ‘rated’ for 15A, but is capable of carrying much more. I felt 10 gauge was the most appropriate, but I am seriously anal retentive (just ask my family). 12GA is probably fine for most applications. A very important point raised by Brian Curry is that 10GA wire it not very pliable and would be difficult to work with. I took that as a challenge.
I purchased some 10GA THHN wire from the local Home Depot. It is stranded, which is a good thing. It is also reasonably pliable (or so I thought). Not convinced this was the best solution, I started investigating further. I came across an interesting article written by Don Eilenberger regarding wire selection. It was critical to my final selection. Don recommends ‘Marine Grade’ wire. Makes great sense. Basically, Marine Grade is wire that has been tinned prior to encapsulation with insulation. Tinned wire is less susceptible to corrosion and electrolysis. It is also much more pliable than the THHN. Ancor makes such a wire and had a “Type 3” that is “Ultra Flexible”. I suppose that is even better.
Now that I have found flexible 10GA wire, I procceded with the remainder of the project.

Wiring Harness:

I choose to make the fuse block live all the time (not switched by a relay). This was my personal preference. I put a 30A inline fuse with the positive cable. I used ‘standard’ crimp connectors at the battery. The fuse box came with crimp/solder connectors, so I use those at the fuse box.


I have a 2004 BMW R1100S. On the older R1100S’s, BMW had two fuse blocks behind the fairing, one on each side. For the 2004’s with EVO brakes, they combined the two and placed it on the left side. This conveniently frees up the right side for the fuse block. I highlighted the region in the photo below.

I purchased some sheet metal from the local Lowes. I drilled and tapped it for the mounting holes for the fuse box. I hit it with a few coats of primer and a couple of coats of flat black paint and mounted it to the location.

I screwed the fuse box to the mounting plate with stainless steel screws and Loctited them in place. He’s a shot of the mounted fuse box.

I ran the feed cable in a plastic sheath just to provide some additional protection from the elements and abrasion.

Note: Check the final photo. When the feed cable is in this position, it interfered with the fairing mounting. I had to make a couple of different routings until I found the final version.

Here’s a shot of the battery end. Note the cable was left long enough such that the ‘Main’ 30A fuse can be easily accessed without removing the fairing. The funky yellow connector in the middle of the red conductor is a Posi-Lock. These guys make some pretty neat devices for connecting wires. The 30A fuse holder is in the highlighted section of the photo. I was not able to find an in-line fuse holder with 10GA leads, so this on has 12GA. The fuse should go before the insulation. Should it get toasted, the Posi-Lock’s should make replacement simple.

Here’s a shot with the Gerbing and PIAA wires in place. I purchased some 12GA Marine wire to use as feed lines for the PIAA’a and you can see the red conductor below the fuse box.

I had to find a mounting location for the Autoswitch and PIAA relay. Since space is tight and I have used most of the free space on this side, I found space on the opposite side of the front end. I labeled some of the things to help give you a reference point. I took a piece of industrial double-sided tape and connected the Autoswitch to the PIAA relay, then ty-wrapped the whole thing to the front infrastructure. I had to run the +12V, Ground, Turn Signal Cancel, and indicator LED wiring across the front to the other side. The Autoswitch needs switched +12V, which I got from the right-side relay box.

Here’s the final shot of the feed wiring. Note that the feed cable was shortened to avoid interference with the fairing.

Here’s a shot from the seat end with the fairing in place. You can see how the fuse is readily accessible. I plan on adding a layer of heat shrink over the cables as another abrasion layer.

Here’s a shot showing the fuse box tucked under the front right side fairing.


This provides an insight to what’s involved in installing an auxiliary fuse box on an R1100S. It will be different (and perhaps impossible) for bikes with two factory fuse boxes. I hope you have found this of value. Please feel free to email me wayne@2zars.com with comments, questions, or concerns.

Last updated 29-Aug-2010