Instru. cluster LED conversion specifics

[Moybin]

The instrument lights in my '99 S appear to be originals (at 80K miles). The 4 bulbs that provide instrument back lighting have grown very dim. The general effort required to get the instrument cluster off the bike means that having a bulb burn out is a really big pain. LEDs are called for (actually, I've been screaming for them).

To make the transition to LEDs I needed to do a major amount of research on the bulbs in the S. This is what I've learned.

The "Parking" bulb in the headlight cluster (who thought up that concept for a bike?) is replaceable by any of a number of colored LEDs from DigiKey. The part numbers are
Blue: 441-1006-ND
Green: 441-1000-ND
Red: 441-1004-ND
Yellow: 441-1002-ND

I'm putting in the Blue just to be different. The bulbs run in the range of $0.99 to $1.60 USD. I believe these are considered a T1 & 3/4 wedge bulb.

The bulbs inside the instrument cluster are type T5 wedge base. This is a Sylvania designation. I bought polarized LEDs from www.surplusled.com. They call them a #74 T5 Wedge base, 12VDC. They cost $0.75 each regardless of color. By polarized I mean there is a correct and incorrect way to insert them in the rubber sockets. I will explain below.

I did a pin-out test of all the pin socket holes in the baby blue rectangular plug at the end of the cable for the instrument cluster. The results are also listed below. To that point, the lights in the Low Oil Pressure and the Low Fuel indicators ARE LEDs!!! From their polarity I determined the polarity for all the other bulbs.

WARNING Will Robinson: I have NOT reinstalled my instrument cluster on OBSSSN, as he is asleep for the winter, surrounded by a mantle of snow. (Meaning I haven't PROVEN that I got the polarity correct for all lamps).

I bought 3 reds, 3 greens, 1 blue and 4 yellow/amber LEDs. The 4 yellow/amber LEDs were to check how well they provided the general back lighting in the cluster. In a word, better than the nearly-gone bulbs, but about half as bright as new filament bulbs. So for now I'm leaving OEM bulbs in those 4 plugs.

All of the other indicator bulbs are in little "tunnels" and require good focusing; just what LEDs do best. The 3 red LEDs go in the Battery and 2 ABS slots. The 3 green LEDs go in the 2 turn signal slots and the Neutral slot. The blue LED goes in the High Beam slot.

They look great! Really bright, good concentration of light, and good color.

Here is the pin-out for the cluster. The Germans use pins 1 & 5 as commons, and they are positive (+), not negative as is common in US autos. Pin 1 is common to all wires with the BROWN/BLUE combo of colors. Pin 5 is common to all wires with the GREEN/BLACK combo of colors. The rest of the pins are fed negative (-) potential. They are:
2 HIGH BEAM - WHITE
3 LEFT TURN – BLUE/RED
4 RIGHT TURN – BLUE/BLACK
6 BATTERY – BLUE
7 NEUTRAL – BROWN
8 OIL PRESSURE
9 LOW FUEL
10 ABS-LEFT – GREEN/YELLOW
11 ABS-RIGHT – GREEN/BLACK
12 INSTR. BACK LIGHTS – GRAY/BLUE

When I get things together I will try and take a photo or two.

[GotRoad?]

Nice reference work. I've been thinking about replacing the sickly looking stock parking bulb with an LED, but was too lazy to look for a replacement. Now you've done it for me. Thanks!

[SergioK]

Wow, very nice!

Interesting that they use negative feeds and positive common.

[Moybin]

UPDATE - POLARITY CHECK

Braving the 20 degrees, wind chill and 2 inches of old snow I went out to the bike's shed and plugged in the instrument cluster. As the battery is on a tender for the winter, not problem with powering things up.

I thought I had the polarities correct on all the LEDs from using my battery charger as a source and the pin-out published above. The Germans must be doing something weird in there, because I had to reverse the 2 blinker LEDs, the High Beam LED and the left ABS LED before everything worked correctly, but IT DOES!!!

The back lighting of the dials is much brighter just switching to bulbs from the turn signals and ABS sockets. Maybe next winter I will design my own tiny printed circuit cards and solder about 5 LEDs to each for the 4 back lights.

Next project may be clear inserts to go behind the side roundels to turn them into signals/side markers......

[JonyRR]

Moyb;
Yes, they are doing something strange and I think it's a bmw thing;
I put LED tail light (not brake or turn, just tail) bulbs in my '94 530I cage, and the wierdest thing happened; no matter what I tried, the 1156 (single filament) LED bulb would NOT light in the oem socket plug (the cages use a plastic cartridge to hold the bulbs then twist into a socket) no matter which way I thrned the bulb. Either I got a bullb set that had ground and hot reversed (LEDs are polarity sensitive) or, of course it'sa bmw wierdness, the hot and ground are reversed for these bulb circuts..strange. I reversed the polarity of the feed wires to the bulb socket holders and they worked! hrew a fault code until I hooked a spare set of runnin' lites LEDs up; then the fault code cleared. umoglich!t

[roger albert]

Hot common to a bunch of the inst bulbs, and switched grounds, is not unique to the new ones. Goes back to at least the /6 series.
Common as a rock in almost all automotive and mobile applications (though the flasher bulb polarity swap is a bit wierd)

Makes perfect sense though, for things like neutral switch, and oil pressure etc. The switch or sensor just needs to ground the sensor wire, and thus the neg side of the bulb. One wire sensors that way (vs 2) and if a sensor wire ever shorts to the chassis or motor, you just get a glowing bulb instead of a bunch of melted crap. Very normal.

[Flatbutt1]

huh? whadya say?

[Joe]

Here are the true schematics for the circuits your working on FYI.Pin 1 is at ground potential at the housing not a hot . I can't seem to locate a BR/BL coming from the cluster just the brown on pin 1 which is ground.

A little advice when working with LED's in a incandescent circuit use a low impedance voltmeter or test light to test circiuts......you need to load them a little or you could be reading voltages through coils or high resistance junctions which will give erroneous readings when it comes to any kind of current draw also it will light led's in the reverse direction of what was intended correct current flow when the circuit is off.

[Joe]

Curious do you know if there is any safety circuit built into the Motronics that senses the oil light or any other safety warning bulb appears as an open now compared to lighting a incandescent lamp. The indicator bulbs are driven directly off of the motronics and it wouldn't surprise me that it might give some fault code or worse won't let the bike run.

[Moybin]

Joe: don't know, didn't try to start the bike, but the fuel pump energized and pressurized the fuel system, so my guess is no problems introduced with the LEDs. As I said in the original post, the Low Oil Pressure and Low Fuel lamps ARE leds.

Also, I think the BR/BL wires are spliced into the harness downstream from Pin 1. Everything is taped at the factory, and the bundle is plenty large enough for that type of goofy splice-craft.

[foobeemer]

Moybin UR THE MAN.

I got a purple and a blue one of these:

http://www.cyclegadgets.com/Products/product.asp?Item=RV

I switch 'em out depending on my mood......like a chameleon!!!