[928uk] analogue clock wiring

[jonathanrackowe at gmail.com]

Hi Phil,

The black wire on the clock connector's pin 2 is a switched ignition +ve supply (term 15). It comes from P25 on the CE panel. As Richard mentioned, that black wire feed is also connected to the light switch - it powers the bulb in the light switch that is always on when the ignition is on. So clock pin 2 is definitely not a signal out connection.

As far as I can tell from pictures of the clock circuit board, pin 2 is not connected to anything inside the clock. However, your experiment suggests that there are either: some electrical components between the (blue/black wire) pin 3 that powers the clock's lighting and pin 2; or a very high resistance between pin 3 and pin 2 (dirt perhaps!); or a fault as you suggest.

Without taking your analogue clock to bits I think that's all that we can surmise. The clock only really requires 3 wires: Red 12V permanent power, Brown permanent Ground, Blue/Black switched and variable instrument lighting power.

Porsche may have initially had something in mind for the black wire ignition on power feed to the clock, but whatever it was doesn't seem to have ever been implemented.

Happy New Year!

Best regards, 
Jonathan

928 GT 1991 Amethyst Metallic
  






-----Original Message-----
From: 928uk <928uk-bounces at lists.928.org.uk> On Behalf Of phil rick via 928uk
Sent: 31 December 2023 17:17
To: richard at ritech-systems.com
Cc: 928uk at lists.928.org.uk
Subject: Re: [928uk] analogue clock wiring

thanks Richard
i just hooked it up to a battery, brown on earth then tried all other
combinations of 12v on the other 3 wires and the black one alters nothing,
if it comes from the light switch i thought it might light the bulb to
possibly keep it illuminated as a belt and braces approach but light only
comes on with the blue/black wire at 12v
BUT
12V on blue/black wire = 0.5V on black wire
0V on blue/black = 0V on black wire
its sending a 0.5V signal OUT on the black wire
or there is a fault on the black wire circuit inside the clock
cheers
Phil

On Sun, Dec 31, 2023 at 4:11 PM Richard Armstrong via 928uk <
928uk at lists.928.org.uk> wrote:

> Hi Phil
> I don't know what its purpose is but it appears to be a supply from the
> light switch - Black
> Then there is a fused supply -red.
> Ground - brown
> and a common lighting supply black and blue.
> Why there should be 2 light supplies I am not sure
> Richard
>
> On 30/12/2023 12:01, phil rick via 928uk wrote:
> > looking online, such as Rogers site:
> >
> >
> https://928srus.com/products/928-641-701-05-70b928-641-701-05-70b-analog-clock
> > it shows the usual 12v , earth and clock illumination and a not used
> > terminal.
> > just removed the one from this 90 and the factory wiring loom connector
> has
> > a wire in the not used location
> > before i break out the wiring diagram's anybody know what this wire does
> to
> > the clock?
> > cheers
> > Phil
>
> --
>