Help, first self-install, HU in 98 Civic

My after-market cd HU was recently jacked from my Civic, but politely, so that nothing internally or externally appeared damaged.  I decided to try installing a new one myself - you can be the judges of whether that was smart.  Anyway, I got a kit and everything, and twisted all of the right wires together, but here's the one weird thing: in addition to the yellow constant 12V wire coming out of the harness, there is another yellow wire spliced off of the factory HU, which is still in the dash (because of the keyless entry issue).  It's probably naive to assume that this is supposed to be the battery wire just because it's yellow too, but it's the ONLY loose wire in the dash that isn't capped.  Anyway, neither that wire nor the battery wire on the harness (am I using that word correctly?) appears to be giving off 12V.  One registers at about .4V and one at .8V.  The ACC wire, however, registers 12V when the car is on.  Long story not so short, when everything is connected, the HU appears to get no power when the car is on.  Is this probably because of my weak battery wire?  Could something the theif did have damaged or shorted something?  The radio fuse is ok.

Thanks a lot, everybody, I appreciate any help you can give.  I hope I was descriptive enough.

-Aaron

I'll bet your main radio fuse is blown.

As far as the second yellow wire is concerned, I am not sure what that is (although I bet there are lots of others on here who will know since the Civic is a pretty common car.)  I am glad to see you are using a wiring harness adapter.

The main ignition wire is red, and it's definitely live.

I checked the fuse marked "Radio/(something else)" and it was intact... I didn't know if there were other fuses that might be to blame.

Ok, I've now checked every fuse in the car except in the special "ABS" fuse box.  There was one blown under the hood marked "Backup (Radio)" or something, and I got all excited, replaced the fuse, hooked everything back up and turned the power on -- nothing.  I took a voltmeter to the battery/memory wire and I'm getting next to no power there.  What else could be wrong?

Thanks a ton for your replies.

Ugh.  I decided I was in over my head and took it into a shop.  Turns out that the only thing that was wrong was that one of the pins on the harness was bent when I attached it to the HU, so the pin snapped when I attached it.  Apparently he had to bypass it.

Weak.