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Bulb control bypass

 
Old 02-26-2013, 07:28 PM
  #1  
SeanR
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Default Bulb control bypass

Got one for Alan/Wally that I need some assistance on and don't think it has been covered.

Customer has installed LED's in his 3rd Brake light and plans on installing them in the rest of his tail lights/brakes etc. Of course the bulb control unit is giving an intermittent warning about the brake lights being inop. Sure we could solder in a resistor but we want to do as the WSM shows on page 90-39. We ordered part number 928 641 610 00 thinking we could just plug and play it. No go, they sent this which is a 12 pin connector with all the bits and a nice do it yourself kit for a nice $50.00. Ack.





The WSM shows this picture:




Now following the wiring diagram for 1988, it shows pin 4 and pin 1 as the corresponding points where current is read? Yea, that's the question. Am I right in thinking that if we bypass this point the brake warning will be bypassed? Now if we jumper pin 2 and pin 3 are we eliminating the warning for the side/tail lights?

Next question, what else is going to be affected if we do this plug in?

Next thought was to just jump pins 8/9 and 20/21 on the central warning computer.
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Old 02-26-2013, 10:47 PM
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Old 02-26-2013, 10:59 PM
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Thanks ZEUS+, looks like this post has all the info I needed.

Originally Posted by Ed Scherer View Post
Last night, at long last, I finally finished up my LED mods. I'll probably do some kind of write-up pretty soon, to add to the already good write-ups that others (like borland) have done recently. Just one more data point to add to the experience knowledge base.

But... one timely thing that I'd like to add now is that the last thing I did last night was to defeat the bulb control module (mine is a 928.641.603.07 on a '90 S4) using a very easy, non-destructive, perfectly reversible technique. You can probably do this in 30 minutes or so. All you need before you begin is:
  • a Phillips screwdriver to remove the three screws holding the carpeted trim piece that, when removed, gives you access to the bulb control module;
  • a wide wood chisel or putty knife that you can use to pry open the connector to the bulb control module;
  • needle-nose pliers, to make it very easy to pull out a couple of pins from the connector;
  • some heat-shrinkable tubing about the size of a drinking straw, to cover the pins after you've removed them

I'll provide some explanation along with photos.


First, here's the lamp control module, after the carpeted piece of trim held on by three Phillips screws has been removed (this is under the dash between the central electric panel and the right-side door, above the LH and EZK modules). You'll want to yank that connector off; it'll probably require a little effort, as it's on there pretty tightly. There are no interlocks; it's just tight. BTW, you don't need to remove the bulb control unit, you just need to unplug the cable.




Once you have the cable unplugged, use some flat, wide-bladed tool like a putty knife or wood chisel (I used a 3/4-inch wide wood chisel) and pry open the connector along the long edge that isn't hinged; it'll open up, revealing the pins soldered to the wires as shown in the next photo. Be careful when you open this up, because some of the wires and pins might immediately pull out. Cover them with your thumb or something so they don't pop out!

Use your needle-nose pliers to pull out pin 10 (RE/WT wire) to prevent the parking/marker light failure signal from reaching the pod and pull out pin 7 (BK wire) to prevent the brake light failure signal from reaching the pod. Pull them well back and snap the connector shut again, being careful that all the pins are pushed in again (visually confirm this by looking into the pin holes once the connector is closed again; I had two pins that didn't seat properly the first time I did this, and I had to open it up again and fix that).




I then used some clear heat-shrinkable tubing to insulate the pins that I removed from the connector, as shown here.




Reattach the connector to the bulb control module. Test that the bulb control module is working to your satisfaction. Then refasten the carpeted trim piece. You're done. Sleep easily, knowing that you can easily reverse this sometime in the future if you need to.
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Old 02-26-2013, 11:00 PM
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Well actually what you want to do with that new housing is simply connect through the relevant pins for Brake & Marker lights.

So for an 88 you need (decent sized wiring):

Link Pins 5, 4 & 3 Markers Right Side

Link Pins 6, 2 & 1 Markers Left Side

Link Pins 14, 13, 11 Brakes Left & Right

OR eliminate the warning signals from the current unit per Ed

OR re-engineer the series resistors inside the unit to the correct values so it still functions now as an LED checker (feasible I think).

Alan
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Old 02-26-2013, 11:03 PM
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Originally Posted by Alan View Post
Well actually what you want to do with that new housing is simply connect through the relevant pins for Brake & Marker lights.

So for an 88 you need (decent sized wiring):

Link Pins 5, 4 & 3 Markers Right Side

Link Pins 6, 2 & 1 Markers Left Side

Link Pins 14, 13, 11 Brakes Left & Right

OR eliminate the warning signals from the current unit per Ed

OR re-engineer the series resistor to the correct value so it still functions a an LED checker (feasible I think).

Alan
Reading further in to Ed's fix and seeing an issue with the cruise control, should I even worry about that in an '88?
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Old 02-26-2013, 11:22 PM
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Originally Posted by SeanR View Post
Reading further in to Ed's fix and seeing an issue with the cruise control, should I even worry about that in an '88?
Sean... I don't have time for a long answer right now, but when you're asking if you should worry "about that," if you mean the cruise control, then I'm thinking, "yes". I'd recommend load resistor(s) for the brake lights to keep the cruise control working. I'm still using my electronic alternative, but that's just because I haven't gotten back to replacing it with a load resistor like I said I would for some safety reasons).
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Old 02-26-2013, 11:30 PM
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You will have the same issue with any of these methods. Porsche just relied on low impedance through the filaments and you no longer have that with LED's

Alan
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Old 02-26-2013, 11:32 PM
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Thanks guys, giving the bulb control/brake light issue a test now. Will test cruise a bit later. I've not used the CC in years so it matters not to me, but might to others. Will report back.
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Old 02-27-2013, 01:25 AM
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ok did the mod that Ed had done on my 88 tonight and i'm happy to report no warning AND all functions of the cruise work like a champ! thanks Sean and Ed!
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Old 02-27-2013, 01:34 AM
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"...AND all functions of the cruise work..."

Make sure that includes cutting off when the brake pedal is pressed.
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Old 02-27-2013, 01:38 AM
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That was the first thing I tested.
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Old 09-17-2013, 05:57 PM
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Would any be able to tell me which pins to pull to disable the "tail lamp" warning on my 82?
I'm not too lazy to look, I did look. I just suck at reading the flow chart.
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Old 09-18-2013, 04:48 PM
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C'mon, Alan. Please!!!!!
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Old 09-19-2013, 12:56 AM
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Bob,

Well - I don't know for sure - but its either pin 6 or pin 8 - one is the brake warning and the other is the tail lamps so you can remove one see if thats it and if not swap. I'd start by removing pin 8 that is the most likely one.

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Old 09-19-2013, 10:43 AM
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Alan,

Thank you! Thank you! Thank you!
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