[V8] High Beams

[Kent McLean]

Greg Furstenwerth wrote:
 >> Kent wrote:
 >> <http://www.humanspeakers.com/audi/headlight-simple.htm>
> I dont really know how to read schematics such as that. 

You don't *need* to relay the headlights. But if you do, it
means you probably won't be replacing the light switch again
in an few years.  It also means your headlights will be brighter,
since they get a full 12+ volts from the battery/alternator,
instead of 11 volts or so they may get through the light switch
and long wires to the headlights.

A relay is nothing more than a switch triggered by an electrical
signal rather than your finger. In use, a little current energizes
a coil inside the relay, which trips (opens or closes) a switch
inside the relay that lets a much higher voltage pass. The headlight
switch trips the relay, which in turn passes power directly from
the battery/alternator to the headlights.

If you still want to know how to read Huw's schematic, read on.
I'll keep this simple, and let the EEs on the list correct me.

Going by Huw's diagram, start at the right side. Find the label
that says "stock high beam wire".  This starts at the light switch
and goes through the fire wall to your headlights.  But Huw spliced
in a relay, using the headlight switch to energize the coil in the
relay that flips the switch inside the relay to power the headlights.

In Huw's diagram, the relay is the black box with what looks like
a coil spring (Slinky) and (use your imagination) a switch inside
it.  In the diagram, Huw cut the high-beam (black) wire and attached
one end (the light-switch side) to the relay.  Notice that black
wire goes into the relay at the coil side, but that coil is connected
to a brown wire that goes to ground.  The rest of the black headlight
wire (that connects to the headlights) is attached to the coil on
the relay's switch side. The other side of the relay switch goes to
to the battery (through a fuse). In the case of the V8, with the
battery under the back seat, the wire is instead connected to the
alternator output (maximum voltage) or the remote battery (jumper)
post (some voltage loss compared to attaching directly to the
alternator).

In other words, from the headlight switch, the old (black) wire goes
to one side of the relay (the coil side), which is connected to ground
with a new (brown) wire.  Another new (red) wire goes from the battery
or alternator +12V to the switch side of the relay, which goes to the
old (black) wire to the headlights.

The other thing Huw recommends is to add a fuse to the new wire
that supplies power from the battery or alternator. That fuse
is indicated by the little black box with the sideways letter "S"
in it found at the top of the diagram. That fuse is to prevent a
meltdown of your relays and wiring if things go bad.

Repeat all of the above for the low beam side, except the old
wire is yellow.

Some people take measurements, then build a wiring harness
on a bench, which is easier than building it in the confines
of the engine compartment. For example:
<http://www.80tq.com/images/Harness%201.JPG>

I think I got it all right, but it's late and I'm tired.

--
Kent McLean
'94 100 S Avant, "Moody"
'89 200 TQ, "Bad Puppy" up in smoke