Installing an accessory fuse box

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Why? My bike already has a fuse box

Yes, it does, but it's not really set up for the use of accessories, or farkles, as they're often called. A new fuse box will allow you to connect other electronic bits such as GPS, radio, or heated gear and have each unit fused individually. This also reduces the possibility of damaging the main fuse box.

If you have only one or two small accessories, you may consider modifying your accessory wires.

Defining terms

You will see auxiliary power supply boxes labeled 'distribution blocks', 'auxiliary fuse boxes', and most likely several other things. The important thing is you want a fuse box, or panel, that will allow you to have a separate fuse for each accessory. That way, if one gets overloaded and the fuse blows, you won't lose everything else.

What kinds of boxes are there?

There are a few different types of fuse boxes/panels. Some treat each attachment point as a separate entity, requiring that power be sent directly from the battery to each connection point on the box (individual circuits) like the Centech AP1. In this case you can daisy chain (make very short connections) the power wires from one connection to the next, instead of running a wire from the battery for each. This article does not cover this type, as it's more difficult to do.

The Eastern Beaver FB-4 also works this way, but it comes in a kit with everything wired for you. This is the easiest reasonably-priced box to use if you haven't done this sort of thing before.

Eastern beaver fb4.jpg

Other fuse blocks have only one connection to power; this connection powers all terminals after the main connection receives power (aka common bus). This is what is used in the photos for this article, the Bussman 15600 Series ATC Fuse Panel. This is still relatively easy to wire up, looks 'cleaner', and is cheaper. Having someone who knows something about electronics to hold your hand is a good idea if you do this, though.

This chart shows the difference between the multiple-hot-wire type (on right) and single positive "common bus" type on left.


There are some advanced boxes that let you wire some things hot all the time and have others that only get powered when the key is on. The Centech AP2 is one of these.

Finally, if you're scared about hooking everything up (you don't really need to be) the Fuzeblocks FZ-1 comes with an internal relay, constant or switched power choices, and only needs a few connections.

Things to buy

All these items should be available at Autozone-type parts stores or electronics shops such as Radio Shack.

  • A fuse box, naturally. See above.
  • A 30 amp, four-pin relay. Numbers on the relay pins should be 30, 85, 86, and 87. Pay no attention to the #87a pin on the relay in the pictures, although a five pin relay can be used without worry, as long as nothing is attached to the 87a pin. Bosch, Omron, and Hella are all good quality.
Relay posts.jpg
  • An inline fuse holder and 10 amp fuse.Take the fuse out of the holder and don't connect anything to the battery until everything is in place.
Fuse holder-3.jpg
  • Several feet of flexible stranded copper wire. 14 gauge is generally recommended. Positive/hot/+ is usually red. Use a different color for ground (negative). Always use stranded wire in auto/moto applications. Pictures show stranded (left) and solid (right) wire.
Stranded wire.JPG Solid wire 2.JPG
  • Crimp connectors
Crimp connectors.jpg
Heat shrink tubing.jpg Heat shrink.jpg
Or the kind of connectors that already have heat shrink on them.
Heat shrink crimp.jpg
  • One machine screw/bolt for the new ground post. Make sure that the ring terminals you plan on using fit over the bolt.
  • Mounting bolts, nuts & washers

Finding a mounting location

For the purposes of this article, we will be following the installation of the Bussman 15600. If you are using one of the Eastern Beaver units, hook the relay up the same, then follow their directions. Mounting will be virtually the same as with the Bussman. In fact, you can use this as a basic guide for any fuse box on most any motorcycle.

The first thing to tackle is finding a place for your new fuse box. In order to know how long to make the wires you really have to figure out where to mount everything, but read the whole article first, OK? This does not mean that you should mount the box yet. As always, try to test everything before mounting, in the interest of saving time if something gets hooked up wrong.

You can mount the fuse box anywhere you want. Our man determined that the best place for him was on the left side, in between the coolant reservoir and the CDI. The mounting location is on the wheel well. There is nothing on the other side to hit with a drill, and you can reach around to tighten the lock nuts on that side. It would be wise to use Nylok fasteners, or something similar, and blue Loctite.


The Buss provides four mounting holes. Only two were used, and the box was mounted diagonally.


Find a convenient point to mount the relay. Remember that 'finding a place to mount it' and 'mounting it there' are two different things. So, don't affix it permanently yet.

You can put the relay just above the stock fuse box, where it's close to the horn circuit and the battery, and not taking up room on the other side. A simple zip-tie will suffice for mounting. The black plastic underneath is the airbox. Absolutely do not drill any holes in the airbox. If that position doesn't work for you, underneath the seat or anywhere on the bike will work. Remember that the shorter the wires the better.


Hooking it up


First, wire up the relay. Why a relay? With a relay, you use the OEM wiring to power the relay, and then put in new wiring for the fuse box. The relay uses a small amount of power (the horn circuit) to turn on and off a bigger amount of power (the new heavier wire) to the new box. This is true for bigger headlights or any other higher-current-draw accessories you want to add to your motorcycle.

Relay terminals

  • 30 positive from battery
  • 87 new positive to fuse block
  • 85 positive from horn circuit
  • 86 ground to the battery negative terminal


  • The main power comes from the battery, through the new in-line fuse holder, to the #30 pin on the relay. The fuse holder wire might not be long enough to reach the relay. If so, crimp in a longer wire. Always keep the unfused portion of a wire as short as possible, so try to hook the fuse holder directly to the battery, then run the longer wire to the relay (after the fuse).
  • Terminal 87 gets hooked to the main positive connector on the Bussman box.
  • Terminals 85 and 86 are the 'trigger' circuit. This is what makes the relay fire. When a circuit is made through this pair, by turning the key on, a switch on the pair 30-87 is toggled from open to closed. When this switch is closed, 30-87 are connected; this connects the battery to the new fusebox and powers your accessories. For this install the positive side (85) was taken from the horn circuit at the stock fuse box. The ground (86) goes to the battery ground (negative).

Installation of the Bussman box

The Buss doesn't provide a 'ground' terminal on their unit. So, you can add a ground post (lower right corner) to compliment the power lead. This is not strictly necessary, but it does make the install safer and cleaner. For your accessories, you could ground them all at different locations around the bike. By putting a ground post on the Bussman you can run hot and ground leads to each device next to each other at the same time, and have them both hook to the fuse box.


To add your grounding post, find a location on your fuse box that will be easy to access and where the bolt won't get in the way of anything. In the example here, the grounding post is in the lower right hand corner. Drill a hole in the plastic that is just large enough for the bolt to pass through. Feed the bolt through from the back side, so the head of the bolt is on the back side of the fuse box, and secure with one of the Nylok lock nuts on the front side. You want the long end of the bolt sticking out, so you can add your individual grounds later.

After you mount the fuse block to the bike, put a wire going from this post back to the negative terminal on the battery and secure it with a k-nut. You can then put all of the accessory ground leads on this post. You can put a couple of accessory leads between k-nuts, assuming the wires don't break from extreme mounting angles.

Use the Nyloks for the body attachments and the top nut on the grounding post because they hold VERY well in a harsh vibrating environment, like on a bike. The k-nuts are good for the middle of the grounding post (holding the ground leads down) because they're metal and grip well on the ring terminals.

Add additional k-nuts as needed (keeping only about 2 ground leads per k-nut) and top it all off with a nylok.

Connect the positive lead from the relay (pin 87) to the positive terminal on the Bussman (red wire).


Sealing the heat shrink connectors with a small torch - DON'T. Lighters and other open flames aren't good around gasoline engines. Use a heat gun.


Next comes the fun part: cutting into the wiring harness at the OEM fuse block. If this makes you nervous, you might want to use Posi-Tap connectors from Posi-Lock. There is a review in webBikeWorld.

Consult the schematic to determine which connection to tap into. Don't use the unused 'accessories' fuse because those two connections are always hot. This also goes for the OEM accessory wires. The horn was the circuit tapped into, since it has minimal draw when not in use. The schematic showed the wire needed to tap was the lower harness brown/white wire. Double-check this by testing the voltage, then pulling the fuse.

This is your 'hot' trigger connection, and goes to terminal 85 on the relay.



The final product. Two accessories are already hooked up, with the 5 and 10 amp fuses. Two more are pre-wired for future farkles. You can also see the negative (ground) wires, connected with ring terminals, on the silver ground post.


Make sure all the connections are connected, mounting points tightened, and you're done. Our home mechanic says, "My Bussman setup cost me about $15, including the relay, wiring and end connections. I've been very happy with it. I've had no averse weather issues with its 'open' design. The two factors that have helped make that occur are its location and the use of dielectric grease."

Wiring the accessories

For hooking up farkles, you can use any of several kinds of plugs that make it easy to quickly connect and disconnect accessory power plugs. There are BMW-style, cigarette lighter-style, SAE 2-pin trailer plugs, and many other coax types. SAE are common, relatively cheap, and weather resistant.

Sae connector.png

The idea behind using these connectors is so you don't have to find your way back to the fusebox every time you want to unplug something. Run the accessory leads from the fuse box to a single convenient location, such as under the seat. Use different-colored wire or another foolproof method that can tell you which wire is for which device.

On the SAE plugs, there are male and female parts. The female is the one where the power pin is covered. This is shown in the diagram.


Crimp female spade connectors onto the female trailer plugs. Connect the power leads to the fuse box male connectors and the grounds to the ground post, with ring connectors. Use the male SAE plugs for the wires to your accessories.