OK... well, it is most likely either your battery or alternator. Do you have another battery you could use? How about a neighbor you could borrow a MM from? Its pretty hard to diagnose electrical problems without a MM.
Yea, often when we mess with are cars and something soon breaks afterwards, its best (and most of the time true) to blame the thing we just worked on. But in this case, unless you just totally forgot to hook up a major ground... I don't really see how you could have messed something up.
With that being said. Go give your grounds a GOOD cleaning. The most import one is the one that bolts to the transmission... clean that really really well... and clean the connection at the bottom just below the battery. Also clean your battery terminals. It could be as simple as that.