Re: <E30> Electrical Repairs

["Brant M. Miller" <brant@xxxxxxxxxxxxxx>]

Scott -

I've looked at my 95 525i ETM lighting diagrams.  Take what I see with a
grain of salt, as I've not actually fiddled with the wires, just looked a=
t
the diagrams.  And, of course, my random thoughts related to a 525i may
have no relevance at all to your E30.  And my comments are for US-spec
cars, not Canadian.

When the Light Switch if set to Headlights, the Low Beam Relay in the Lam=
p
Control Module is energized, without regard to whether or not the High
Beams are energized.  So the Low Beams should be on at all times that the=

Light Switch is set to Headlights, even when the High Beams are energized=
.

When the Combination Switch (located on the control column - the
dip-switch/flasher) is set to either Flash or High Beam, the High Beam
Relay in the Lamp Control Module is energized via the Crash Control Modul=
e.
 The Flash position on the Combination Switch is powered directly from th=
e
Front Power Distribution Box.  The High Beams position is powered from th=
e
Light Switch - the same wire that feeds the Low Beam Relay, however, use =
of
High Beams should not cause the Low Beam Relay to drop out.

So there appears to be no reason why your Low Beams would switch off
momentarily after use of high beams.  They do not ride on the same relays=
,
etc.

The Lamp Monitor system ties the various lighting circuits together in a
way that is not easy to understand.  It may be that some aspect of that
circuit is the problem, but I doubt it.

There has been discussion on the Digest about corrosion in the connectors=

beneath the Lamp Control Module in the Front Power Distribution Box.  The=

increased resistance causes flakey results - which you have.  It is
possible that the extra current flow related to use of High Beams causes
the Low Beam Relay to trip-out until a built-up voltage can bleed off. =

Both relays share the same ground.  Can you put a volt meter on the relay=

ground wire?  Or, more easily, are you sure that your Low Beams stay on
until the High Beams are switched off?  If they drop out sooner this theo=
ry
may be reality.

A final thought re the 525i system:  Although the High Beam Relay appears=

to be wired in a straightforward manner, the Low Beam Relay is not.  The
switch is double-pull, one for each light, and has a transitor device
across the two pulls - perhaps to provide power to both lights, even if o=
ne
pull fails.  And there is a connection to a "High Omhic Resistor For Cold=

Monitoring" - whatever that may be!!

I doubt I've helped you much, but it has been fun looking at my ETM.  I
could spend a couple of years with it and still not understand.  Some
instruction on how BMW engineers think would help!

Brant

>Date: Fri, 01 Jan 1999 20:59:41 -0800
From: Scott Miller <sdmiller@domain.elided>
Subject: <E30> Electrical Repairs, Stereo Upgrades - Progress Report...

Headlights:  Symptom - with low beams on, switch to or flash high beams,
and when switching back to low beams, the headlights go completely out
momentarily before the low beams come back on.  What I tried - replaced
both low and high beam relays with new Bosch relays.  No improvement.=3D2=
0
Attempted to replace the turn signal / high beam / low beam switch with
a used switch, . . . etc.<

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