borland

Pulled the module on my 90' S4.

Quite easy to do on the 90' and later cars. The module resides just to the outboard side of the glove box. Simply remove a trangle shaped carpeted piece (three screws), open the glove box door and remove a couple more nuts that hold a bracket in place, and the module drops down along with a alarm module.

The module on my 90' has a later part number, # 928.641.603.10. Taking the cover off.....

- same printed circuit board as in the photo previously posted,
- same component count. Only difference is the ICs are of a different part number.
- uses Telefunken U4791B and 4790B special automotive application ICs.

So, different part number but same basic circuit.

borland
90' S4

Alan

Borland & Ed - just swapping the load resistors should be enough. The lamp control module just senses that the voltage drop across the resistor when the load is turned on is enough to indicate the bulb is not burned out (and presumably also is not so much you have too powerful of a bulb installed).
So there is a voltage window comparator... however its configured.

So a higher value Rx should work - you'd need some trial & error to determine but a ratio of the Bulb Current:LED Current should be close to the Needed Rx value:Existing Load Rx value. You will not need anything like such a high power load Rx - 2W ceramic should be perfectly OK for a typical LED bulb (but maybe not for a 3W LED version).

Another way to do this is to monitor the voltage across the load Rx's when the correct bulbs are active - then match that voltage drop for your LED's

Alan

Ed Scherer

Great minds think alike, Alan. And ours, too, apparently.

From an e-mail I sent borland on Tuesday:

I'll probably start messing with this next week. Rather busy with the holidays right now (compounded by the fact that it's my wife's birthday today).

borland

Alan, You can view the datasheets here:

http://www.datasheetcatalog.com/data...9/U4791B.shtml

http://www.datasheetcatalog.com/data...9/U4790B.shtml

Ed Scherer

I see from the data sheets that the threshold voltages are 53 mV for the U4791B and 8 mV for the U4790B; that's the main thing I wanted to know. Now it's just a matter of a few details like what shunts are hooked to what bulb sockets, what LEDs we're using and their current flow at normal voltage, a little math, some adjusted shunts, and Bob's your uncle.

BTW, borland, thanks for taking the time to pull your module and get the IC info. It's nice having the right data sheets for the ICs used in our 90s.

Alan

Ed - a downside of making that change is that if anyone ever replaced an LED bulb with a regular 21W incandescent a lower power rated higher value load Rx will probably fry and even if sufficently rated it would significantly limit the brightness.

But the bulb warning should alert! at least briefly!

I'd mark the back of the lamp cluster as appropriate "LED Bulbs Only"

Alan

borland

I'm finished with the mod and experimenting...

To verify cutting the traces defeats the bulb monitoring, I cut the traces for the Marker Lights. It does disable the digital instrument cluster's "Tail Lamp Failure" message. On the cars with digital display, you have to start the engine and wait for the digital display message. Headlights or parking lights need to also be turned on also.

Later, I also cut the trace for the brake light and verified the same defeat for the Brake Lights monitoring.

Restoring the traces is easy if you keep the cuts narrow. All you need do is to tin the copper plating on both sides of the open trace, de-flux the cut area with a solvent, and then apply a drop of solder from the soldering iron. The trace will wick off enough solder to bridge the gap. Confirm the joint is restored with a ohmmeter.

I also modified my module to allow an LED replacement bulb for the Third Brake Light. It works great; no faulty warning message. With this mod, if the other incandesant brake light bulbs fail, the warning feature will still work. If the LED fails alone (>10,000 hour typical life, so highly unlikely), then no warning.

Here’s an annotated photo describing the LED Third Brake Light circuit board mod:



http://img187.imageshack.us/img187/5...lledmodgt4.jpg

I’m not recommending anyone do this to anyones car, as it defeats the car’s original design safety features. Just documenting what I did and the results.

borland

Instead of REPLACING the shunt resistors, you could place a high quality operational amplifier in the circuit, for each shunt, so as to boost the voltage drop across the shunt, before feeding it to the special purpose IC.

Op-amps are great for such an application, as they can easily be set to a prescribed gain. Take a look at "Non-Inverting Amplifier":

http://en.wikipedia.org/wiki/Operational_amplifier

Happy Holidays Everyone!

borland
90' S4, Slate Metallic

Lizard928

looking at the wiring diagrams for the 85/86 by removing the wires from the plug #8 &#6 it should disable the warning for stop lamps and running lights. I will go try this in alittle however.

borland

For the third brake light, here's the LED that I settled on. Perfect fit. It's the brightest 1156 that I could find, nice pattern and seems brighter than the 3W Luxeon. Price is for two bulbs, but you only need one:

http://cgi.ebay.com/ebaymotors/NEW-V...8063QQtcZphoto

BC

Ken - where is your page on defeating the warning system compuyter under the dead pedal?

PorKen

Brendan,

I don't think I ever posted on it by itself. I used small male terminals to jumper the sensor to the light on the black and yellow CWS connectors. Each sensor/light are on the same connector.

I only did the most important functions, oil pressure, coolant temp, etc.

BC

I remember you taking pictures of it. Did you take any pictures?

Lizard928

Well I pulled the #8 & #6 pins out of the plug for the bulb controller verified that all the lights worked normally and I now have no stop light warning from not having a 3rd brake light.

justin

Whats the best way to defeat the bulb module on an 80 MY? I installed LED brake light bulbs and I am staring at a " stop light " warning in my dash.