Schocki

This topic has been discussed on Rennlist previously. Somebody on PFF-Online in Germany modified his 928 to daytime running lights. The modification is easy and done in a couple of minutes. Here is my write-up and some pictures.

Relay III on the main curcuit board is empty and can be fitted with a standard relay. Porsche uses a relay with an extra diode to prevent running the fog lights when not intended (thanks Allan for the clarification). I took a standard relay and soldered a diode between Pin 85 and the coil.

Here is how it works: As soon as the LH-ECU energizes the fuel pump relay the fog lights come on as daytime running lights. Relay III receives power from the fuel pump relay output.

The ground power supply for the relay is provied by the position of the headlights. As soon as the headlights are out ground power to relay III is interrupted and the fog/daytime running lights are turned off.

Bottom line: The daytime running lights are an excellent indicator if your fuel pump is running or not

Here is the Porsche part number: 141951253B Relay 14,11 € (Should be around $20)

Modification should be possible on any MY 90 or younger.

Location of relay III on the MCB



Daytime running lights on, fuel pump running


Headlights on ground power supply to relay III interrupted.

Dean_Fuller

That is very cool...so all one does is add the relay??? No wiring needed?

Schocki

Yep, plug and play

Alan

Schocki,
What you say is almost right... it certainly basically works. The headlight connection is to the headlights on (high or low beam) connection inside the relay. There will be an effective ground for the coil via the headlight filaments (either one since one is always connected to this point) as long as headlights are off. This will only work if at least one the filaments selected are good - two burned out low beams or completely missing HL bulbs means the fogs won't work with the headlights off. As soon as the headlights turn on (must be up) the fogs will go out - since there is no voltage difference across the coil.

The diode in the Porsche DRL relay is to avoid the fogs coming on when not intended - the fuel pumps will never run due to this since the relay coil in series limits the current to ~150 mA.

When the fuel pump is off and the headlights are on the coil will energize supplied in reverse by the headlights and grounded through the fuel pump(s). So if you turn the ignition on (engine not running) with headlights on the DRL fogs will come on.. this does not happen with the stock DRL relay.

Probably a rather minor issue - but thats what the diode is for. Adding a diode on the back of the CE panel in series with the coil connection would allow a regular Bosch SPST relay (...'53 type) to work exactly like the stock DRL relay does.

Alan

worf928

One thing I'm missing here I think...

An empty relay socket is not wired to anything. Maybe position III is different?

Alan

This socket is wired on all '90 & newer cars as Schocki indicated. Except in specific locations that required it (e.g. Canada) it was never populated - but is considered an optional extra.

Alan

Alan

Personally I have tried this out but I removed it again. I don't want to run DRLs all the time - but would like the option for certain times of year only. The factory system has the fogs always on after starting as long as the HL's are off & the engine is running .

I'd like my DRL's to be defeatable and to include the marker lights as well. I have a design for this but have not installed it yet since I'm pending swapping my front lights (Fog/Aux) for a ROW set (like Schocki's pictured).

Alan

6mil928

I thought the same thing as Worf maybe a title change is in order.

"Daytime running lights modification possible on all MY 90 and younger cars... "

worf928

Ah. This then is what confused me (emphasis is mine):

So, if younger than '90, the socket will need to be wired-up as if it was 90+.

Hilton

You could just get the appropriate relay that British S4's got in '88 and '89.

Known as the dim/dip option, it changes the headlight/driving light behaviour to meet a UK ruling that existed briefly. In position 1 the headlights come on with a dim dipped beam, but stay down, and the driving lights all come on on the front/rear bumpers. In position 2, the headlights actually pop up, and get normally bright.

Amusingly, it does mean UK cars from 88/89 can operate the headlight washers with the lights down

borland

I've been looking at LED DRLs using the S4/GT/GTS "Additional High Beams" instead of the fog lamps. The LEDs are not as bright as the stock H3s, but the additional high beams are an overkill anyway. Here's my idea for the Central Electronics Mod on my 1990 S4 ....

Break one connection and install high current diode. This allows Flash-to-Pass for the additional high beams when the headlights are on...



Getting the Flash-to-Pass to pop-up the headlights during daylight hours is somthing I haven't worked out yet.

osiig

Thanks for this write up. I searched eBay for 431 951 253 G, which is the part number for relay III, and found one for Audi. The electrical schematic is the same as for the Porsche part incl. the diode. I just popped the relay in place on my 1994 GTS and it works as specified i.e. the fog lights come on when the engine is started regardless of the position of the headlight and front fog light switches.

Bertrand Daoust

I noticed on Schocki's car that it is the outside lights that is used for the daytime running lights.
Are those the fog lights?
Is it that the Euro cars have fog lights on the outside and the driving lights on the inside??

On my car, the fog lights - daytime running lights - are on the inside.

Vilhuer

Its ROW vs US/Canada thing.

Bertrand Daoust

Thanks for the clarification.