Porsche 928 Electrics

Electrical information & supplies for late model 928s

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Daytime Running Light System:

This is a planned project - not yet fully completed...

Factory Spec Option:

My GTS already has a provision for a DRL capability with the addition of an optional relay, however it only operates the front fogs whenever the car is running - I don't really like this mode.

My Desired Operation:

I think ideal DRL's should be operated automatically when desired by driver choice (e.g. switchable) and should always include rear and side markers as well as optionally front fog lights for good all round visibility. There should be some driver indication that DRL's are active rather than normal headlights. It should be possible to leave the DRL system in the desired state and have it engage upon starting the car. A DRL off mode should disable all DRL functions


I plan to replace my front fog light switch with a switch body from a headlamp switch. This will give me a 3 position turn switch instead of the current fog light push switch (2 position ). The new switch will control my automated DRL system as follows:

Position 0 = Off - The DRL system is disabled.

Position 1 = DRL1 - Marker Lights automatically light whenever the car is running

Position 2 = DRL2  - Marker Lights & front Fogs automatically light  whenever the car is running.

My expectation is that I would use all the positions based on need.

The DRL2 position alone activates the fog lights regardless of the light switch position.

The DRL2 position and Lighting 2 position operates fog lamps & head lights (either high or low beam) The fog lights are configured in the stock ROW configuration where they stay on with high beams

I have the design already completed for a 1990+ configuration only.

Dashboard Indicator:

When the new fog switch is in position 1 or 2 and main light switch is in positions 0 or 1 the existing green 'marker light' indicator will come on in the pod. This will go out whenever the ignition is off & light switch is in position 0 or when the ignition is on and the light switch is in switch is in position 2 (headlights)

I like this functionality because:

- I can turn off the DRL mode whenever I want
- I can still force the fogs lights to go on whenever I want
- I will always have front/side/rear markers also on in any active DRL mode
- I can leave the DRL switch in any position I want and allow the ignition to automatically switch it
- The dashboard indicator reminds me when DRL mode is active (as with HL 1 mode)
- 'Flash to pass' still always works (at least the driving lights flash on)

The only thing I think is less good is that now the adjacent headlamp & front fog lamp switches have the same operating mode (3 position twist). It would be possible to relocate (say to the bottom left position) - but the fogs and reset switch also have a similar operating mode in the stock configuration (push momentary/push lock). Instead I will ensure there is a color difference via the use of an LED.

The features I describe utilize the existing fog light relay for fog light switching and an extra relay to switch the marker lights, they are both controlled the same way.

related to this change I had previously installed HID lighting (6000K) with reflector adaptations for my fog lights described elsewhere - this is great for DRL use since is is bright and lower power (35W Vs. 55W stock). I also have upgraded (to 70W) & color temp matched H3 bulbs for the driving lights. Given the 55W per bulbs and both on design for the ROW fixtures - this stays inside the stock power envelope (105W Vs. 110W stock) and my usage of high beams is never extended enough for this to be a major thermal concern. I have also transplanted a set of ROW fog light/driving lights and these are configured the other way around: the fog lights are outboard (where they belong) with driving lights inboard. The reflectors & lenses are also slightly different (better). These fixtures also combine an amber front marker bulb in the fog light lens which is active with the other markers.

This was a rather complex, expensive and time consuming modification. However I think it along with my H4 headlights with electric adjusters and partial marker light conversion to LED's completes the blending of the best of the lighting options from the USA & ROW models (heavily leaning to the ROW configuration) with sensible HID & LED deployment.


Copyright (c): Alan Moore 2006, 2007, 2008, 2009       Page Updated: 04/03/2009