Mrmerlin

Alan thanks for the info.

Also to note the headlight motor is grounded to the chassis,
so make sure the mounting bolts are clean deoxit is also a good idea

scottpeterd

What should we do? I've one year into a 1979 928 and have gone through most of the electrics. Currently working on the instrument pod circuit board.

Bought mine last year in Vancouver. Drove 7K miles down to Mexico and around the US and back to DC. On more than one occasion the headlights went out (at speed in the desert). Much fun...

I've got spares for all the other relays EXCEPT for the .127. I do a lot of driving at night.

Could another stock relay be modified with diodes? I see in the pics how the 'A' terminal is separate. Perhaps an external diode with a spade terminal on a short piece of wire?

Alan

It is a relatively normal relay with 2 inputs to the coil each with a series diode to isolate them from each other. Of course this means it has to have an extra corner input pin for the second coil input.

If I needed to fix this:

It would be functionally equivalent to use a standard SPST Bosch style relay and add both the diodes outside the relay.

You'd need to remove the wire feeding the Internal Diode-B connected on socket pin 86 (corner pin on this relay). This will go to the anode of your new external Diode-B. Also remove (repurpose) the wire feeding Internal Diode-A on socket pin A. This will go to the anode of your your new external Diode-A. Then the cathodes of these new 2 external diodes will be connected together and connected to the pin that was labelled A on the original diode. (This is actually normally the 86 terminal location on Standard SPST Bosch relays)

For a 78/79 USA car there are always at least 2 open fuse slots Fuse #2 (Aux Headlights) and Fuse #34 (Rear foglight). I would install my diodes there. Take a torpedo fuse and cut the element out of the center - then solder a diode* in the gap (*from radio shack get a 1A 100V(+) PIV diode) - now you have a neatly packaged diode that won't easily get damaged and is easy to test. This way it's also easy to connect to - just use standard terminals. These fuse holders are totally open - they are not bus connected in any way so you can easily wire to both ends to make your connections.

Overall I think it would have been better if Porsche had done something like this originally Vs. all these special relays with extra diodes. You basically pay >$50 for a diode or 2. Meanwhile Porsche has to stock a bunch of different SKU relays that really aren't that different - everybody loses!

Alan

scottpeterd

Alan,

Thanks for confirming that. I like the idea of using the spare fuse sockets for the diodes.

I was thinking of an wire harness that would allow me to relocate the relay with the diodes attached to it.

Your solution is much more elegant.

Thanks...

cgraner

https://rennlist.com/forums/928-foru...l#post18281427

Alan

Thanks for posting that link - I thought about it a bit more over the last few months based on some PM questions on this topic.

Anyway - Roger seems to have a source with full functionality now. (see the thread)

Alan