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Thread: Front/Rear Fog Light Switch/ Using a Hazard Switch for Fog/Associated Wiring

  1. #1

    Front/Rear Fog Light Switch/ Using a Hazard Switch for Fog/Associated Wiring

    So I finally completed a long awaited installation of my front and rear fog lights. The wiring diagrams are quite simple (see below). I decided to wire mine up per the euro configuration so that I could run my lights any time the license plate lights were energized. Otherwise you can only use them when the headlights are in low beam mode.

    The trickiest and most time consuming part was the drilling of the hole in the dash to accommodate the switch. The trick here is to get the accurate center of the hole in relation to the cigarette lighter and the rear window defroster. Since there is very little space to work with, you have to use a small flexible metal ruler. I wanted to be as close to center as possible so that I could use a small hole just to fit the switch shaft. I could have made it larger to make it adjustable, but I couldn't see making a sloppy hole. In the end I found that the center of the cig lighter and the defrost switch was right at 4" center to center. So I put a piece of painters tape across the lighter socket and the area to mount the switch and marked the center of the lighter. I then measured the switch location 2" from this to give me the horizontal position.

    Since the dash is slanted slightly, you can not mark the vertical position in relation to the shaft of the other switch, as it is sloping downward and all thus lower the position too low. You also have to use the straight dash trim below the switches as a reference, because there is not a sharp edge above the the switches to measure from and it does not to be very straight in my opinion. I do not remember what this distance was, but I guess they could all vary and should always be checked.

    After making a punch mark on the center, I drilled a 7/16" hole using a uni bit. Note that if you have a radio, you need to protect it from metal shavings. I used more painters tape.

    Since I did not have an early "fog light" switch, I decided to figure out how to use a pre 69 hazard switch instead as a fog light switch since I had 2 of them and they have the same lighting mechanism for the face as the fog light, just a different color (clear in my case). So I do intend to get the correct green emblem and rubber cushion.

    Wiring the light was also tricky, because the wriring diagram uses "NR, N, 58, -", and my hazard has "K, 1, 2, 3". Using the 2 stage fog light switch for a 78, I was able to match that terminals 1 and 2 matched N and 58. NR is dedicated to the rear fog light, and I am planning on it to share a terminal for the front fogs since my switch is a single stage. Because the later fog switch is plastic it requires the "-" terminal (ground). Do not hook a separate ground to the switch as indicated below. Instead, use the #3 terminal for the indicator light in the knob. What I could not figure out was, what was "K" for? Nothing happen when checking the continuity with either open or closed condition. Then I was able to figure out that the K terminal is for the dash lights for night time illumination.

    The easiest wiring part was the rear fog lighting. There was already a harness in the car from the rear to the front, and this is true for all early cars and I think until 83. The confusing part here is that the wire at the light is green with black tracer, and the wire I found behind the dash was white with a green tracer. Notice in the wiring diagram that it changes color after the first terminal from the lamp. Since the terminal connecter already had a "piggy back" terminal, I used it as the connection on the switch, and then connected the feed from the relay onto the piggy back.

    The relay I used was an standard relay plug with 5 wires. I used 4 as per the diagram and the only wire I had to make was from the switch to the fusebox and the relay ( about 15 feet of wire and a couple of terminals) I had enough wire on the really plug that I was able to wire the fuse block wires directly without any extensions.

    When the switch is on, both front and rear fogs are active. The other option is to get a two stage switch and make them independent, but this was not important to me since it would require me to use a later switch that would not look right.

    I could not find all of this in one setting, so I hope that someone finds this useful and using other options for switches and making their own wiring harness to and from the switch. Let me know if I can be of any help for anyone if you need it.
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    Last edited by orange911; 03-09-2012 at 07:06 PM.
    Olin - Member #1375
    1972 911T

    -117 Light Yellow -15x6 Fuchs (9120/M400) -S Appearance (M470) -5 Speed Transmission (9590)

    Options added
    -Houndstooth Sport Seats (M409) -Rear sway bar (9228)
    -H4's -BTB Fog Lts (M429) -Amber TTG Driving Lts (9420/M432)
    -380mm Steering Wheel -Becker Mexico -Roof Mounted Luggage/Ski Rack (9503)
    -A/C (M559) -Rear Fog Lt (M571) -Rear Wiper (9290) -Wheel Trim (M426) -Footrest (9563)

  2. #2

    Rear light mount

    I felt like I should cover mounting the rear light since it was left out of the earlier post. I had the original mount duplicated with a piece of stainless, and used 6 mm allen bolts with lock nuts on the back. Mounting the rear fog light was a challenge due to the tight fit between the valence and the muffler. If I were to do it again, I would take off the muffler. The fog light I used was not a Porsche part and thus used the mounting for ground. This meant that I had only the hot wire as a lead. I disassembled the light and removed this wire and fed the two wires from the harness into the light. You must cut the spade connectors and put new ones on after inserting into the light. There is no connector for the ground wire in my light, so I put a small ring terminal on the end of the ground wire and slipped it on top of the bulb before inserting into its slot (which also helps ground).


    1) be sure to feed the lock washer and fog light mounting nut through the wiring before feeding the wiring through the mounting bracket.
    2) use a grommet to prevent wire chaffing through the bracket.
    3) wires will fit through the mounting stud, but I could not get the sheathing to go. Cut the sheathing back to give yourself plenty of wire inside the light to work with
    4) I mounted my light with about 1" of separation between the light and the bumperette.
    5) do not put the end terminals on until you have everything mounted and ready to put together, or you have to cut the terminals off to get the light back off.
    Olin - Member #1375
    1972 911T

    -117 Light Yellow -15x6 Fuchs (9120/M400) -S Appearance (M470) -5 Speed Transmission (9590)

    Options added
    -Houndstooth Sport Seats (M409) -Rear sway bar (9228)
    -H4's -BTB Fog Lts (M429) -Amber TTG Driving Lts (9420/M432)
    -380mm Steering Wheel -Becker Mexico -Roof Mounted Luggage/Ski Rack (9503)
    -A/C (M559) -Rear Fog Lt (M571) -Rear Wiper (9290) -Wheel Trim (M426) -Footrest (9563)

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