Replumbing 12V to the Instrument Cluster

this is not new, i found it on a french 928 site:












I have started on mine, doing one here one there as i can.

I've written up a tech article for submission and publication to the OC. The fix is conceptually simple, but requires studying the schematics for each model year 928 as many changes were made over the years. My article doesn't provide exact instructions as they can be very different for different model years.

For my 1979 928, the instrument cluster is powered by an ignition switch controlled line (15 circuit in 928 schematic speak).

What the fix was for me was to cut that 15 circuit (wire) before it plugs into the instrument cluster. That circuit became the "low current control" voltage for a 12V relay (the other end of the low power relay control is connected to ground).

Next, a tap was made from a central "12 V always on" (30 circuit) spade that was available in the central electric panel (fuse panel), a 5A fuse was added in series for safety. This relay switched circuit now becomes the 12V circuit input to the instrument cluster.

The ground connection to the instrument cluster was cut and connected to a separate wire that was run to an available ground spade in the central electric.

It sounds easy, but it does require studying the schematics and finding the correct wires/circuits.