Re: Baffling Headlight Wiring Problem

[Huw Powell <human@nh.ultranet.com>]

[most useful information snipped]
>     To make a long story short and avoid the painful reliving of the
> excrutiating details, there is enough voltage leakage into the high
> beam circuit to trigger the relays on low beam. The bulbs don't last
> long, but they sure are bright.
>     With the relay harness connected, there is 7.5 Volts in the stock
> high beam circuit with the dimmer switch in low beam position.

Look, I'm not really sure what's happening, but maybe I can at least add
some directions to your search.

1.  I have noticed that the headlight wiring on my cars, L and H
signals, is *grounded* when off.  So, if the "-" connection to your
relay is being lifted from ground by return current from the low beams,
that would trigger your relay.

2.  it "sounds" like everything you did, you did right - but I'm
suspicious of your grounds.  Try setting everything up, just for one
side (other side hanging loose...), turn the low beams on and add one
item at a time, if you can.  first the "interconnect" you built to get
you high beam tap.  Measure all voltages, and resistance to ground of
wires that are supposed to be grounded.  A - Then try pluggin in the
relay. B - Then add the connection to the high beam.  Next do it again,
reversing steps A & B.

I bet somewhere in this process a light bulb will go off - hopefully the
one over your head, not in the lens.

Another trick is to stick a diode in line with the relay trigger wire,
in the direction you *intend* the current to flow.

Bosch relays take about 9 volts (I think) to trigger, but will stay on
until the signal drops below 6 volts.  This can introduce weird problems
when using more than one relay if a stray signal can find a path through
two relay solenoid coils to ground - that will kepp the relays on when
they are supposed to be off.

Good luck!

-- 
Huw Powell

http://www.thebook.com/human-speakers/audi-main.htm