You will need to take out the parts of the ignition and put in new parts. It is usually best to trust a mechanic to do this for you.
A person an change the starter on a 2002 GMC Sierra 1500 by disconnecting the battery and removing the retaining bolts on the starter. The original starter is then disconnected from the wiring and a new starter reconnected.
That would be inside the polar control unit
The 2003 GMC Sierra-2500HD has 16 valves.
The 2003 GMC Sierra-1500 has a V6 engine.
The 2003 GMC Sierra-2500HD has a V8 engine.
The 2003 GMC Sierra-1500 has 12 valves.
The 2003 GMC Sierra-1500 is a gas-powered vehicle.
The 2003 GMC Sierra-2500HD is a gas-powered vehicle.
The 2003 GMC Sierra-1500 has overhead valves (OHV).
The 2003 GMC Sierra-2500HD has overhead valves (OHV).
The 2003 GMC Sierra-1500 has a 5-speed manual.
The 2003 GMC Sierra-2500HD has a 5-speed manual.