2003 Chevrolet Silverado Electricail problems

My truck is drawing power and killing the battery sometimes it takes a week sometimes days. It had a HD radio that I replaced with just a regular $50 radio from Walmart. We thought we had it pinpointed to a power seat drawing because that what the tester was showing the draw was from. But it turned out that wasn't the problem. The antenna to the radio had a splice in it so I replaced the adapter and without pluging in the adapter to the radio it seamed that it was drawing power from the antenna through the adapter so I unplugged the adapter and it worked fined for about 2 weeks and know it is starting to act up again, the radio fuse is pulled no adapter wiring in either. But this morning it wouldn't start again so I got mad and punch the dash where the radio used to be and without having the ignition on the truck fired right up. Could it be the ignition switch the is drawing power?