I recently changed my battery on my Legacy.  Everything was fine for a while after that, then one day I went to start it and when I turned the key, I lost all power to the car.  I looked under the hood and as soon as I touched the positive terminal, power came back, it started up just fine, and I got home.  The next day when I went to leave, the same ting happened.  Again, I basically tapped the positive terminal and power came back, but this time I figured I should take some extra time and make sure this wasn't going to keep happening.  Upon closer inspection, the connections were a little loose, so I tightened them up.  All good, right?  I thought so, but then when I started it, the ABS, brake, and VDC light all came on and stayed on.  I looked up what could cause this and couldn't really find much.  Some of the troubleshooting I saw was to disconnect the battery, then connect it again, but that didn't work.  Has anyone experienced this or have any ideas on what the cause could be?

kinda seems like either the battery's post is intermittent in the case - or possibly you have a cable with a lot of corrosion under the insulation.

If you over tighten the battery top mount they seem to break before they strip a screw. (so watch for that)

 

Its possible its buggered up now. 

 

I would like to 2nd on the possible corrosion issue. That can make things go haywire.