need 20-30 amp supply

I think youll be hard pressed to find a 20-30 amp supply anywhere near the dash. Why not use the ignition wire to trigger a relay, and get current directly from the battery (fused of course) If you look in the relay section of the board the exact way to set up this setup (bad pun) is explained.280 Bhp Jap

Amd Duron1000

512mb/80GB

Navi/Mp3

Still tinkering.

This is the relay im talking about Connect ignition wire to 85, and ground to 86 Then run a heavy enough wire with a 25 amp fuse from the battery to terminal 30 and connect your Ham radio to 87, with appropriate grounding. Now, when u turn on the ignition the current will flow from battery to terminal 30 to terminal 87, and your radio will have power.280 Bhp Jap

Amd Duron1000

512mb/80GB

Navi/Mp3

Still tinkering.