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I believe both Series 3 and 4 Spiders have a light delay as in delaying turning off. I thought I'd see what I could find. Short of knowing a particular car or cars and going to a Pick-A-Part and removing the light which hopefully the delay part would be attached, it seems to be a do it yourself situation.

Just like Colonel Klink, "I know nothing (regarding electronics)."

So thought I'd give detailed instructions complete with photos so that you too can build one or two or...and sell them to me. I'll add that I want to add two LED's under the dash for entry lights. One of these gizmos should work fine for that. It might be nice to have a light or two in the trunk also.

I believe I pulled out all the pertinent information:

The way it works
I won't bother you with technical details, but if someone is interested just let me know and I'll explain in detail. For now just the basics. There are two stages: first one is delaying and the second one is fading. When you open the door the light turns on. You get inside and close the door, but the light stays on (delay stage) for an adjustable period of time (0-40 sec. for the values in the scheme, but you can easily modify that i.e. put a bigger capacitor) so you can see where to insert the key or do whatever you do when you get in the car, then fades away (fading stage) with an adjustable speed. If you connect the ACC wire (which is entirely optional) when you turn the key to ACC position the light turns off (actually fades) even if the delaying stage is not over (it cancels the delay stage).

Setup
The SR1 trimmer pot adjusts the delaying time (the period that the bulb is at full intensity) and you have a "witness" LED that is lit during the delaying stage; that way you can set it visually to whatever duration you like. When the first stage ends (marked by the LED not being lit anymore) enters the second stage - fading. The SR2 trimmer pot adjusts the fading time (or speed if you prefer)


The first image depicts how the dome light switch is usually connected (depending on the make and model of your car the connection may be different in which case you'll have to figure it out).
The second - the schematic and the connections to the dome light switch.
The third (and last) is an actual image of the finished product made on a PC board (you can get those from radio shack or your local electronics store)
Hope someone will find this useful.

*******

I have added two small resistors; 470ohm in series with SR1 and 1k2 in series with SR2 in order to have a small impedance when the pot's is zero so as the capacitors discharge or charge through some impedance instead of straight through wire (they're limiting the current a bit); they are not critical and as long as you don't set the pots to zero you don't have to worry. Indeed I added them after the scheme was done and I forgot to draw them in... my bad, but it should work without them given that they are a kind of... let's say added protection.

You can adjust both the entry delay and the duration of the fading to your liking. For me it was 20 seconds entry delay (I timed myself how long it takes to get ready and added 5 secs), and set the fade duration to 3 seconds. The slow fading is also romantic!
 

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1966-2013
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Cool. Having the fade out can be a nice feature if the only light is in the mirror as for some reason a bright white light in your eyes that just 'snaps' off is a bit more evil to ones night vision than one that fades. (yes, I realize that night vision takes more than seconds to kick in, but a light that goes out instantly tends to leave spots in your eyes vs one that gently fades out)

Query:
The diagrams are nice, but other than the obvious use for the black wire, where do the other wires go according to color?
Or is it literal in that top to bottom in the drawing is top to bottom on the part?
(in which case the diagram represents the top picture of the unit, but rotated 180 degrees counter clockwise, correct?)
 
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