Airhead Tech Pages


Date: Tue, 30 Aug 94 10:28 PDT
From: druth@erg.sri.com
Subject: Re: Auxilliary Lamps wiring question

In message (199408301541.IAA16146@ogma.autodesk.com) you write:
Has anyone put auxiliary driving lamps on an '92 GS? I'm going to be helping a buddy put his lamps on his GS and I'm looking for advice.

I'm in the process of installing dual 55 watt PIAA lights (one driving, one fog) on my '91 R100GS/PD. These are really nice, small, light lights. They are approximately 3.5" spherical, are made of a plastic composite material, and weight about 9 ounces each. They're the ones that sort of look like they have a fish-eye lens. They're halogen, using ion-projector technology, suposedly superior to ordinary halogen, but then that may just be marketing hype. I do know that they are used as stock driving/fog lights on many high-end Japenese cars such as Lexus, etc. They cost about $175 per pair (plus tax), but you can only buy a pair of driving lights or a pair of fog lights. I found a buddy (Dave Doudna, also on this list) who was also interested in mounting a pair so we bought one set of driving lights and one set of fog lights and then split the sets.

I'm going to mount mine to the `roo bar (fairing exoframe) alongside the fairing side panels. PIAA claims, that due to their fog light's superior cutoff, it's not as critical to have the lights mounted low as for other fog lights. Still, everything else being equal, lower is better for fog lights.

I'm going to contol them with a 3-way switch (SPDT center-off) for the following effects:

  1. both auxiliary lights off,
  2. both auxiliary lights on,
  3. lights wired into the standard light circuit so that when the main headlight is on high beam the driving light is illuminated, and when the main headlight is on low beam the fog light is illuminated.

If one wants to use a standard BMW switch, one has several choices:

  1. For a instrument panel mounted switch, buy the heated handgrip switch.
  2. For a right-side switchpod mounted switch, buy the Euro-spec right-side switchpod (~$70). This has a 3-way switch used in Europe for turning the headlight and parking light on/off. It is in the same position as the high/low beam switch on the left-side switchpod, except that it moves left-right instead of up-down.

I'm using the switchpod mounted switch.

The following crude circuit diagram shows the switch side of the relay circuit.


Driving
 Light
   O------+-------+
   |      |       |
   V      |       |
          |       *              \
          |                       \                   Fuse
          |                        \                  /\
          |          *----------* " *-----------+---*/  \  *-------* 12V
          |         /             "             |        \/
          |        /"             "             |
          |       / "          Relay #1         |
          |       * "          SPST-NO          |
  Fog     |       | "                           |
 Light    |       | Relay #2                    |
   O----------+---+ SPDT                        |
   |      |   |                                 |
   V      |   |                  \              |
          |   |                   \             |
          |   |                    \            |
          |   +-----------------* " *-----+     |
          |                       "       |     |
          |                       "       |     |
          |                      \"       +-----+
          |                       \       |
          |                        \      |
          +---------------------* " *-----+
                                  "
                                  "
                                  "
                                  "
                                  "
                               Relay #3
                               DPDT (one pole unused)



The following show the coil side of the relay circuit:



                            +--------\/\/\/\/\/---------+
                            |       Relay #3 Coil       |
                            *                           |
                      SPDT                              |
   switched 12V  -------*-----                          |
                    center                              |
                       off  *                           |
                            |                           |
                            +--------/\/\/\/\/\/--------+
                                    Relay #1 Coil       |
                                                        |
                                                        V


The Relay # 2 coil is wired into the existing high-beam circuit as follows:


                  ____
                                                                  to
    12V ----------*  *--------------------+-------------------> highbeam
                 existing                 |
                 highbeam                 |
                  switch                  /
                                          \  Relay #2
                                          /   Coil
                                          \
                                          /
                                          |
                                          |
                                          V

Notes:
1) Ground is designated by:    |
                               |
                               V

2) I suggest using identical DPDT relays for all three relays and don't connect
   the unused pole or throw.  It makes future trouble-shooting easier and you 
   only have to keep a single spare.

3) Circuit connections are denoted by either + or *

4) The relay coils acting on the switches is denoted by:    "
                                                            "
                                                            "
                                                            "

5) If anyone wants part #s for the relays I used (bought from Digi-Key) let
   me know.

I hate drawing ACSII schematics!!!

-- Doug Ruth         | SRI International    | '91 BMW R100GS/PD | AMA #:197665
-- druth@erg.sri.com | 333 Ravenswood Ave.  |    Lic. #:BMBLBMW |
-- Work:415-859-3860 | Menlo Park, CA 94025 | '87 Honda XR600R  |
-- Home:415-969-5071 |                      |                   |


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