I suspect that the wires to the clock are:

- ground
- constant power (to run the clock)
- backlight power (when you switch on the headlights, possibly adjustable if that's in the car..)

Not sure if the colours on the back of the multi-gauge panel match with the clock wires though, so the brown wires may not be right at the moment either. (does the lighting inside the dials work?)

I'd suggest getting a switched power feed from the radio connection. If you have adjustable dash lighting then you can't use the (back)light feed for the volt-meter as it would not make sense..

I'll see if I have a wiring diagram somewhere that shows this, perhaps it helps.

Bye, Arno.