[s-cars] Headlamp relay wiring weirdness - Insight needed

[Dave Ellis]

As part of my headlamp rebuild project this winter I installed a new
wiring harness with relays for the 9011/9012 bulbs on my '93 S4.
Everything's together now and I was able to test it last night, but I've
run into some strange behaviour that I'm hoping the group's collective
wisdom might help sort out.

When the headlamp control stalk is set to the first or second notch, the
low beams come on as expected (DRL equipped Canadian model) since the
lower voltage for the DRLs is enough to trigger the low beam relay and
bring on the low beams.  But when I move the control stalk to the third
position which should be low beams on (and for which I expect to see no
change with relays installed), instead of no change the low beams remain
on but the high beams also come on.   Usually both highs come on, but
occasionally only one or the other does, usually when the ignition is
off.  Weird.  Pushing or pulling the high beam stalk has no further effect.

At this point I've ruled out any wiring mix-ups, and I have no real
ideas other than a vague notion it may be some sort of ground loop
problem.  It appears to have something to do with the higher voltage
sent for normal low beam operation as opposed to the low voltage
normally sent to the lows for DRL operation.  The fact that sometimes
only one high beam comes on when the engine is not running (and so lower
voltage is supplied from the battery rather than from the alternator as
would be the case with the engine running) leads me to suspect some sort
of voltage sensitivity related issue.

Anyone ever run into this type of issue before?  Any ideas?

Thanks!
-Dave