I was wondering, what is the best program to draw very detailed diagrams of my CarPC?

I need to draw:
- Car Components (Battery, Doors, Trunk, Bonnet, Seats, Dashboard, etc.)
- CarPC Components (LCD, SUB Hub, Amplifier, Speakers, Crossovers)
- Electrical Components (Switches, Relays, Buttons, Fuses, Distribution Boxes etc.)
- Wiring of different kinds (Remote, 12v+ constant, 12v+ switched, 12v-) with direction of current flow

I was using Visio, it's is very easy to use, but it is rather limited when it comes to drawing things like this...
It has poor support for electronic diagrams. I couldn't find my kind of relay, there is no build in "understanding" of elecrical circuits or of elecrical current flow, no cables with different sizes (4 AWG or 12 AWG).
It is like drawing an elecrical diagram in MS Paint
It also doesn't have 3D support - it's not vital, but it's easier to represent a car (especially when it comes to wiring in the dashboard or under the carpets) in 3D...

Can I find a better program for that? maybe some Visio addon?