Relay Box

When I bought my K75 in 1986 I ordered the BMW driving light kit offered as an accessory. That kit had two rectangular Bosch lights - one driving light for high beam and one fog light for low beam. I installed the kit and rode the bike that way for many years. Later, I wanted more light so added a set of Motolights which I used with low beam, and I used two driving lights with high beam. The K75 had a round headlight in a rectangular headlight shroud so there was room to mount two Fiamm horns and four 30 amp relays inside the headlight shroud.

On my R1150R, it was difficult to find a good place to cleanly install four relays, fuses and associated wiring which was easily accessible. I decided to use a "project box" to mount in the cockpit area above the handlebar clamps.

The box contains four 30 amp relays - one each for the high beam, low beam, driving lights, and Motolights. Two power leads fused at the battery come in to the box. One supplies the high beam headlight and the Motolights. The other supplies the low beam headlight and the driving lights. Since the system is designed to run the driving lights with high beam and the Motolights with low beam, at night a single blown fuse will still leave some forward illumination - either the headlight beam or the auxiliary lights. It would take both main fuses blown at the same time to give me a "blackout."

The power distributed to the lights is also fused, in the box. There are separate relay-switched, fused circuits for the high beam, low beam, driving lights, and Motolights. The relays are controlled with signals from the original factory installed headlight circuits. The auxiliary lights are further controlled by the two switches mounted in the end of the box. The switches are center-off switches. One switch controls the Motolights and allows them to be Off, On with low beam only, or On all the time. The other switch controls the driving lights. They can be Off, or On with the high beam only .

Three wiring bundles exit the bottom of the box. One bundle is a yellow-white-brown trio which connects to the OEM headlight circuit and provides control inputs and ground for the relays. Power is drawn from the parking lamp bulb circuit with a 4th wire to provide key switched +12v for the Motolights "on all the time" mode. The OEM headlight socket is disconnected from the bulb. Spade connections connect here for the inputs to the relays. A new NAPA high temperature H4 socket (NAPA Part #LS-6235) connects the relay output to the headlight bulb.

The second bundle is the power leads from the battery to the relays. The third bundle is the switched power from the relays out to the lights: white and yellow to match the original color coding for the headlight and blue and purple for the driving lights and Motolights respectively.

All of the wiring in the box also follows the same color code, along with red for +12v power and brown for the relay ground. Designing the circuits was easy. Finding the right components and their physical layout was the challenge. Actually building it was pretty straightforward as I followed my hand drawn color coded wiring diagram.

The box mounts to the top of the handlebar clamps with two bolts threaded into holes drilled and tapped into the clamps for this purpose. The control switches are convenient on the end of the box and the fuses are easy to get to if the need arises. I did select fuse holders that require a Phillips screwdriver to open instead of simple knob type covers. I think there is less chance for a problem with "busy fingers" with this design. I left room on the cover for a volt meter but haven't installed one yet.

I have installed two Pilot pencil beam driving lights and a set of fork mounted Motolights. The switches control light operation. The driving lights each have a 55 watt H-3 bulb and are adjusted to be used with the headlight high beam, or they can be off. The Motolights each have a 35 watt, 8 degree, MR16 bulb and are adjusted 3 degrees down from horizontal per Motolights aiming recommendations. They can be on with low beam, on all the time, or off.

Normal night time operation is the driving lights on with high beam and the Motolights on with low beam. Switching from high to low beam is controlled with the OEM headlight beam switch. Normal daytime operation is Motolights on as conspicuity lights with either high or low beam.

Running the high beam headlight with the driving lights and the Motolights all on is awe inspiring. The 700 watt alternator will easily carry all 240 watts of forward lighting if necessary. I don't think 5 lights is legal in most states, so this is not normal operation - but it is nice to have it if I need it. Now to experiment with higher power H-3 driving light and H-4 headlight bulbs. The wiring, fuses, and relays were selected to allow a 130/90 H-4 headlight bulb, 100w H-3 driving lights, and 55w MR16 bulbs all at the same time.