Posted 08 February 2010 - 01:16 AM
You want an unswitched circuit to power the fuse box. I'm not familiar with the wiring on a 1990 so I can't offer guidance there.
However, if your car has a modern digital radio (with memory presets), the stereo will have an unswitched, permanently live feed. You can tap into that wire to power your clock via its insulated spade terminal. The spade terminal on the clock's case is for an earth wire. That can also be connected to the earth for your stereo. Lastly, there is the clock illumination. That can be tied into your gauge cluster illumination. I leave suggestions on that to others more familiar with later cars.