its probably not the ground wire issue. heres a quote i found from another site:
"9 times out of 10 it is the alternator.
When a truck gets as old as ours are - people have "jury-rigged" wiring over the years.
A common thing to do is to wire up the alternator so it is always hot - which will drain the battery over a period of time (usually overnight - but since you have a new deep cell optima, it takes a week). An alternator should only be on when the key is on.
You don't need to take the main terminal off the alternator - just unplug the field wires. These are the ones going into the back of the aternator (for the brushes). The brown wire is usually the one you need to disconnect (if the brown wire is still there). "
http://www.chevytalk.org/fusionbb/pr...hp?tid/162688/
try disconnecting the battery and see if it dies, if it doesnt then try disconecting the wires that snap onto the side of the alternator. you could also test the voltage on the wires when the key is off, if you get voltage try to find out where that wire is going and wire it to the accsesory power. make sure its fused, im not sure what amps the fuse should be.
if you have any other questions post em I like to troubleshoot its my favorite thing to do, good luck!