|Basically your headlight switch currently directs the
current (with the main light switch on) to the headlight bulbs via two wires: a yellow
which sends current for low beams and a white wire which directs the current for high
beams. There is a relay upstream of the fuse panel which seems to be in place to allow the
flasher switch to turn on the high beams rather than the low beams. It does not have an
effect in this set up as it is before (electrically speaking) the relay you are going to
What in effect you have to do is to use the yellow and white wires coming off
of your dimmer switch on the steering column to switch a relay which in turn sends current
to the lights and the only current going through the switch is that required to switch the
relay.....which is sfa and not any strain on the contacts.
I chose to use the Porsche relay set up ( you know, the little round ones which you
find in the front luggage compartment), mainly for compatibility (hate to have to carry
extra spares around) and as I wanted it to look stock. You can get the socket from your
Porsche dealer, it is part number 901 612 333 00 and has 5 wires connected to
30 Switched current supply (red)
85 Ground for switching current (brown)
86 Power for switching current (grey)
87 Switched current output (relay not receiving switching current AKA default position)
87a Switched current output (relay receiving switching current) (red/white)
Now on to the installation of said relays for both high and low beam, which
means of course you will need two of the sockets and relays (black ones, not the red
ones....they have an internal diode in them which is not necessary.
For low beam relay control.........the stock low beam wire, namely the yellow
wire, goes to the power side of S5/S6 on the front fuse panel (they have an internal
connection) and it gets connected to the grey wire on the relay. The brown wire on the
relay goes to ground, pick a likely looking existing brown wire as the 911 is pretty
consistent in that brown always means ground, or you can do what I did and tie it to the
big ground connection near the battery, but then again I am anally retentive and neurotic,
you may want to take an easier one. The red wire on the relay needs to pick up power from
another fuse on the front panel (I used S17) and is the new power supply to the
headlights. The default (87/red and white on relay) is free..........not connected to
anything as you dont want the power from S17 going anywhere if the low beam
headlights are not on. Make sure that there are no bare wires coming out of this (I cut it
short and then put heat shrink tubing over it).The other red and white (off of 87a) goes
to where the yellow wire used to be, at the power side of S5/S6.
Viola, relay controlled low beams!!
For high beam control, it is basically the same except that the power from the
dimmer switch for high beams is white and connected to the power side of S7/S8. It then
goes to the grey wire on its relay (86), brown to a ground (85), red wire to a fuse on the
panel (S17 is fine), default red and white (off of 87 on relay) is not connected, other
red and white (87a) is connected where white used to be at the power side of S7/S8.
Note that the power (red) does not need to have a fuse on the input side of things
(i.e. you can connect it to the side which is closest to the battery electrically
speaking) as you have 2 fuses for each headlight in S5 through S8. Minor risk that the
relay will go nuts and cook something, but I was willing to take the chance..
Note also that the plastic on the relay holder is fairly stiff and can be a pain
to fit into the panel......I just boiled some water and soaked the relay holder (minus
relay of course) until the heat made the plastic soft and then it popped in no problem at
all. Resulting effect is that it all looks stock and is (IMHO) "right".