Stevenwr

I have a 88 S4 and was wondering if anyone replaced the light bulbs in the seat memory switch? If so what bulb size are they and how to get to them.

Thanks.

StratfordShark

I have the seat memory switch in front of me now, as I'm investigating why the position 1 button no longer operates. I also have the Sheet 7 (for my MY91) seat and memory wiring diagram open too.

The 'bulbs' behind the individual numerals are actually LEDs. The big memory button has an incandescent bulb behind it.

I can't see a non-destructive way into the switch either, so sorry no idea of the exact specs of the less/bulb!

Let me know if you get into it...

StratfordShark

Oh dear I'm feeling very stupid now! Was just searching threads and I posted photos of disassembled switch 9 years ago. And it turns out my P1 problem is intermittent and I had it back then! The switch comes out of the trim piece that clips into door just by pulling apart the big tabs. Then you can carefully lever the actual switch out of its rectangular shell (it's held in by four tiny plastic tabs at corners). The LEDS and bulb are soldered in - I can't see a non-destructive way to further disassemble pcbs in order to desolder them!
https://rennlist.com/forums/928-foru...ry-switch.html

Alan

Generally the LED's are reliable - the switches easily get gummed up though. Try flushing (off the car) after some disassembly with switch cleaner. The memory switch bulb is never illuminated unless the switch works - the LEDs should work though .

Alan

StratfordShark

Thanks Alan. As luck would have it I had same experience as 8 years ago - having failed to fix the P1 position switch (going by switch not closing at pins), with the switch reassembled and back in car the P1 started working for first time in months!

While I had the switch apart, I could check that mechanically the metal membrane switch was closing with a positive action when pushed, so I'm pretty sure the problem is solder joint to that switch. Even so next time the P1 fails (I'm the only one who drives the car, so have 2 spare positions anyway - I'm just OCD about things working) will try your idea of flushing the switch through. The new switches if you can find them are $100+!

Ed Scherer

The following two posts might be useful:

• a post describing replacement of the seat/memory switches' yellow LEDs and the incandescent bulb with white and red LEDs, respectively
• a post describing how bad solder joints in the seat/mirror memory/motor controller caused intermittent seat/memory backlighting failures (and how to fix it)

Disassembly of the seat/memory switch/indicator assembly to the point where you actually get the LEDs and incandescent bulb out is non-trivial, but possible. Be prepared to do some de-soldering in some very confined spaces.

For seat/mirror switch backlighting issues, I'd suspect problems with the controller (i.e., the second bullet above) before anything with the switch backlighting bulbs.

Stevenwr

Thanks for the reply guys. I have the switch taken apart to the point where I can see the bulbs but there is a black plastic piece surrounding the 3 yellow LED bulbs that I can't figure out how to remove. When I press the #3 button it doesn't light up but the long oval button lights up red and the seat and mirrors go to the pre-set position. Nothing happens when I press the #1 & #2 button.

StratfordShark

What's the correct operation of the lights? I thought all the position buttons are backlit when car lights are on, and the red pilot light just lights as a demanded position moves to memorised position. Do the position number yellow LEDs in fact operate separately? I'll need to go into dark garage now to check! Ed Scherer's post implies separate operation.

StratfordShark

I just shut myself in dark garage for a look. The numerals are all backlit with sidelights turned on, so all the LEDS must be lit. I hadn't noticed before, but then am rarely driving my S4 in the dark!

MainePorsche

...Ed Scherer's post implies separate operation.

Yes, is such.

StratfordShark

So if separate operation, when do the LEDs operate individually? Maybe they are brighter when pressed, but you can't see with your finger on the buttons!

Alan

I too have only ever noticed the back-light operation - but they are individually wired to the controller so it seems there should be some individual function - but as you say it doesn't make sense for it to be one active only when pressing the button.

Logically it would make sense that it would show what memory was last recalled (e.g. what memory does the current seat position correspond to). But for me it doesn't seem to do that.

Alan

StratfordShark

I can't remember now how the LEDs were drawn on the wiring diagram - that would show whether they had individual function. I won't be home to consult that sheet till next weekend now. The owner's manual is no help - it only described function of memory 'pilot' light.

But it feels as if should be individual function. The switch has 7 or 8 contacts (I think one is dummy plastic pin), of which 1&4 detect button press (the different positions have different series resistor, with direct connection to P1). One terminal for memory pilot light, so plenty spare to drive LEDs individually!

Alan

When I say they are individually wired - I mean I know that is the case - no speculation, so there was some intent there.

Alan

StratfordShark

My apologies Alan - I read it as referring to the labels at seat controller end that Ed Scherer speculated were for individual LEDs.

So the puzzle remains regarding how they behave other than simple backlighting. As with your observations in your car, I couldn't discern any behaviour indicating currently selected memory despite having all 3 position buttons and the LEDs working.

I think I'm going to disassemble the switch again and reconnect it for any clues - can use paper clip end to push position buttons so won't have 'digit obscuring digit' problem.

These cars have a lot of depth to them haven't they?