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RE: <E28> Dome light timer

Wherein I said:
>>Hi All,  Does anyone have experience with the time delay on the dome light
>>going
>>off?  I beleive that they should stay on for 6-10 seconds after you close the
>>last door.  On my car the lights go out immediately.  TIA
>
>At least on E30s, the interior lights are operated directly by the door
>jamb switches on all but the driver's door, and there is no delay for those
>doors.  The driver's door operates the interior light via a time delay
>relay.  The delay occurs only if the relay has been "armed" by a grounding
>contact on the  outside door handle (so the delay does not occur when the
>driver exits the car).  So if the light comes on when the driver's door is
>opened, but does not remain on for a few seconds after being closed, look
>for a faulty grounding contact on the forward edge of the door handle
>(inside the door cavity).  The edge of the handle rubs a bent copper
>contact.

Then Don E added:

>Sometimes, sometimes not. My E28 sometimes DOES leave the light
>on for about 10 seconds after EXITING the car.. and sometimes
>doesn't and it sometimes does leave the light on when I EMTER the car..
>for a short period of time, or until I turn the key.. and sometimes
>it doesn't.
>
>If it seems erratic - it is. Never bothered me enough to think
>about tracking it down..
>
>I suspect it is SUPPOSED to do both - consistantly.. but..
>


Well, Don, it sounds like you have *two* problems.  One results in it not
always delaying when it should, and the other causes it to delay when it
shouldn't.  If both problems were fixed, it would be consistent.  But if
you don't care, I wouldn't blame you! ;)

An inadequate ground contact on the door handle or intermittent opens in
the door jamb connector, in-door connector, or wiring can all make the
delay function intermittent.

And moisture in any of these connections can cause electrical leakage from
the delay relay "arm" input lead to ground, making the relay
*super-sensitive*.  This could easily cause the delay to occur when you
EXIT the car even if the intended delay arming function was not working
right.  Moisture-related problems are usually intermittent. The arming
circuit on this relay has a very high impedance, so it doesn't take much
moisture in a connector on this circuit to make it wonky.  On our E30, for
example, even minor electrical glitches, like the operation of a door jamb
switch on any *other* door, would turn the relay ON, and the leakage kept
it on.  Drying the connector fixed it.

One of the frustrating realities of modern equipment is the many *possible*
faults that can occur.  Each one has some "signature".  When you have
multiple problems, the number of different symptoms that can be observed is
huge.  That's why diagnostics are always so much fun!

- -Paul Reitz
BMWCCA #1167