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HomeTech Articles >

Guest Technical Article:


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 install.

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 it............they are:

Terminal Function

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) (red/white)

87a Switched current output (relay receiving switching current) (red/white)

Now on to the installation of said relay’s 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 don’t 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".

Dennis Kalma

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