I originally wrote this piece some seven years ago in 1995. Finding that the last of my modified bulbs burned out one filament the other day, I had to make some more up, which gave me an opportunity to revisit the article and to make it more useable.

Note that most if not all states require that any taillight or running light on the rear of a vehicle be RED as per D.O.T. guidelines unless it is used to illuminate the license plate.

The idea is to increase visibility of a motorcycle by the addition of two permanently illuminated rear running lights. Added to the central red light this gives three rear facing lights, allowing car drivers to triangulate on three light sources rather than one, enhancing their depth perception and improving the biker’s safety

I had fitted Full Scale Designs’ running light kit to the front and rear of my K100LT. A nice installation on a not so nice motorcycle, now sold and unlamented. The installation described here is not as elegant as FSD’s but is equally effective. It has the merit of being much cheaper. You can also buy a ready made kit from www.run-n-lites.com for $30 plus a $50 core charge (as of August 2002). I cannot find a listing for FSD.

The instructions that follow are for the rear lights only and apply to my 1975 R90/6; a quick check of wiring diagrams should determine their applicability to earlier and later models. I doubt they would differ much. I never did this fix to the front lights, opting instead for a headlight modulator. Plug and play models are available from Kisan Technologies for about $100 – make sure you get the SLI (slim) model for your /6 as the regular one is about 0.25 inches too thick and prevents replacement of the headlight lens. Kisan is at: www.kisantech.com. This device does more than anything I have seen to enhance the visibility of a motorcycle.

In these litigious times, you are warned that everything in this article was written for my benefit. If you chose to follow any of this, you are solely responsible for any outcomes.

Tools:

• 10mm hex wrench
• Flat file or Dremel tool
• Phillips screwdriver
• Soldering iron
• Needle nose pliers
• Wire strippers
• Ohmmeter (not essential)
• Paint (fast drying BMW touch up lacquer is fine)
• Spade connector
• crimping tool

Materials/costs:

• 4 Sylvania 1157 clear bulbs – from any automotive store – under $4
• Packet of Radio Shack spade and lug insulated connectors. About $1.75.
• Solder
• 24″ of insulated wire, similar gauge to that used by BMW in its wiring – probably free

Sylvania 1157 bulbs:

Unlike the single filament bulbs in your bike, the Sylvania (or equivalent) is a two filament bulb, distinguished by two blobs of solder on the base. One blob connects to the element which will be lit at all times when the brake rear registration plate light is on (side or main on the handlebar switch on the /6), the other will be lit only when using the turn switch to indicate directional change.

Instructions:

1. Protect your diode board: disconnect the battery negative terminal at the right hand of the bike where the speedometer cable enters the transmission – 10mm wrench.
2. Make the bulb fit the BMW holder: the 1157 bulb is keyed to prevent incorrect installation in its bulb holder. Unfortunately, this key gets in the way of the BMW one filament socket. With the solder blobs facing up identify the lower of the two spigots on the side of the bulb base and carefully file flush using a small flat file or Dremel tool. Remove the single filament BMW bulb from the reflector/holder. Check that the modified 1157 bulb will now slide into the BMW bulb holder readily. If it does not, you have not filed the spigot flush.
3. Identify the weak filament: Using an ohmmeter – it reads 2.4 ohms, compared to 0.8 ohms for the bright-filament; mark the side of the bulb with a spot of paint next to the weak filament solder blob. If you have no ohmmeter: remove the BMW bulb, insert the modified 1157 bulb so that only one of the solder blobs contacts the spring base. Reconnect the wires, connect the battery, turn on the ignition and try the turn signal. Note brightness. Remove bulb and reinsert so that the other solder blob contacts the spring again noting the brightness. Mark the solder blob which gave you the weaker output.
4. Remove the reflector: first remove the two Phillips screws holding the amber cover to the base of the turn signal assembly on the back of the bike. Then remove the bulb/reflector assembly and remove the positive wire (blue with a red stripe) from the center and the negative (brown, ground) from the connectors on the back of the reflector. You do this by pushing the plastic circular retainers against their springs, allowing the wires to release. If you skipped step 1, prepare for a short circuit and a new diode board ($$$).
5. Solder in the running light connector: cut off a 2″ length of wire, strip both ends, and solder one to the weak filament identified in 2, above. Take care with the soldering iron – too much heat can fry the element. The key is to make a small soldered connection so that the wire does not protrude beyond the periphery of the base, making installation in the holder impossible. Using the BMW touch-up lacquer, place a generous dab of paint on this newly soldered connection. This will reduce the chance that the soldered terminal will be in circuit with the spring in the bulb holder. Crimp an insulated spade terminal to the other end.
6. Make up three more bulbs by repeating steps 2 through 5: One is for the other side, two are spares.
7. Identify the power source for the running lights: remove the two Philips screws holding the red cover to the tail/registration plate light. Ease out the reflector/bulb assembly, but do not disconnect any of the wires. Identify the gray wire with a black stripe – this provides 12 volts to the license plate light (one half of a two filament bulb, the other half serving as the brake-activated stop light). The gray/black wire is held in place by a spring.
8. Get at the power source: remove the two 10mm bolts inside the taillight cover; if your bike is on its center stand, you can easily reach under the rear fender, and hold on to the nuts and washers to prevent loss. Pull up on the cover and move it aside.
9. Rout the power wires: two cables exit the cover through a grommet and enter the horizontal chromed steel tube (“crossbar”) which carries the directional indicators. Cut 6″ more off the 24″ of insulated wire – you will need these for the other running light and its spare – and thread the remainder through the hole in the crossbar in each direction so that it exits in each turn indicator housing. You now have the crossbar with your new wire exiting both ends and excess hanging out of the grommet hole. Thread this up through the grommet and the hole in the base of the stop light housing into the housing, tie a temporary knot in it and reassemble housing, grommet and crossbar. Reinstall assembly on rear fender.
10. Connect the power wires to the source: undo the knot in your new wire, cut the wire, strip both ends, twist ends, cover with solder for neatness (like the factory does) and insert under the same spring which holds the gray/black wire identified in 7, above. This wire is powered whenever either the parking light or headlight is on. Finger pressure or careful use of needle nose pliers is required. Replace the brake light/reflector and red cover.
11. Adjust the springs in the bulb holder: using the needle nose pliers, carefully turn up the ends of the contact spring on the back of the indicator reflector/bulb holder. This will ensure that the spring can only contact one of the two solder blobs on the 1157 bulb when it is inserted.
12. Insert an 1157 bulb with soldered ‘tail’ into the holder ensuring that the unsoldered element contacts the spring in the reflector/holder.
13. Complete the power wire: first cutting off any excess, strip the protruding wire stuffed through into the bulb holder base in step 9, and crimp on the other half of the crimp connector. Attach the ‘tail’ to this connector. Reattach the blue/red wire to the center connector on the back of the reflector and the brown wire to the side connector. Replace the bulb holder/reflector- there is lots of room in there for the ‘tail’ if you tuck it in neatly, and replace the amber cover and Phillips screws.
14. Repeat for the bulb on the other-side.
15. Place the two back-up with ‘tails’ in your tool tray under the saddle. Reconnect the battery – light finger pressure only on that 10mm bolt, or you risk stripping the soft aluminum thread on the engine. Start the engine and switch on the headlight.
16. Ride safe!