Wherever the manufacturer put it. Exact location can vary, but they'll typically be in front of the flywheel.
Remove and replace the starter.
The starter solenoid is bad.
on top of the starter
The starter for a 2002 GMC truck is located on the passenger side of the block by the transmission.
There is no such thing as a 310 Chevy truck.
The starter or battery could be weak. The weakness will cause the starter to turn too slowly to start the truck.
There is only one starter per truck. If you follow the positive battery cable from the battery it will lead to the starter.
starter solenoid is connected to top of starter
This truck uses three different engines, all with slightly different starter mounting. All starter replacements are pretty similar though. Most importantly you must first disconnect the negative battery cable. Raise and support the vehicle. From under the vehicle remove the large and small power wires to the starter. Remove the starter mounting bolts Remove the starter. Reverse procedure for installation.
the solenoid is on the starter the relay is on the fight inner fender
It is on the top of the starter, It's part of the starter.
Might be you starter or starter rely and/or coil.