First of all make sure the battery is fully charged and the connections are tight. Grab the battery cable terminals with your hand and try to turn them, if you can turn them by hand they are too loose, tighten them.
Next, with the key on start check for voltage at the purple wire at the starter solenoid. Also, make sure you have battery voltage present at the big red cable on the starter and the starter bolts are tight. Grab the starter and try to move it, if you can move it tighten the bolts.
If no power to purple wire with key on start check for voltage at the purple wire coming out of the start relay 62 in the fuse block underhood.
If no voltage there check the start fuse #43 30A in the fuse block underhood.
If fuse good and still no voltage at purple wire, check Ign Fuse #23 15A in the fuse block underhood.
Let me know what you get so far and we will go from there.
Wiring Diagram 05 Chevy Col M30 click here.
Wiring Diagram 05 Chevy Col MA5 click here.