prelude wiring/electrical problems

I had my 91 prelude stolen a while ago and the battery, seats and stereo was taken. Now i am frying to fix it but have a couple problems.

1. With a brand new battery in there, it goes dead if the car sits for a few days.

2. I tried installing a pioneer head unit but it didn't turn on. I looked up the wire colors on install dr. and soldered all the wires. There were 2 wires left over coming out of the car and the power antenna wire coming out of the head unit. I checked both the fuse on the head unit and the "radio" fuse in the car. When i measure voltage on the "acc" lead i get between 6-9 volts. Voltage at the battery is good, 12.6 volts.

What could be wrong?

Any help is appreciated.

update:

the pioneer head unit is brand new

and the car starts fine if it sits only for hours.

6-9v at the acc lead is not enough to power on the new receiver. Also, the fact that the car will start after a few hours, but not a few days, tells me that you have a short some where that's draining the battery. Were the seats power? You may have a cut wire. Do you have a wiring diagram?