Okay, as I said.... you have 1 singular wire that goes from your battery to the bulkhead. Look at this diagram.....
http://farm4.static.flickr.com/3645/...c2a8064d_o.jpg
It doesn't matter that the wiring schematic is truck specific. GM didn't reinvent the harness for their van line. The exact terminal going into your firewall might be different, but there is still 1 singular wire that runs to the bulkhead, which will be in your engine compartment exactly behind your fuse panel.
Start at the bulkhead and check for 12 volts there. No volts = blown fusible link or broken wire. If you do have power, get under the dash and ensure that wire is intact, all the way to the ignition switch. No power when the ignition switch is turned on= faulty ignition.