Need advice on how to replace the serpentine belt on a 2002 Chevy Silverado 2500 HD Diesel?

hope this helps? should do it for you.
https://www.justautorepair.com/multimedia/1-belts-diagrams/detail/129-diesel-belt-routing

Google images is the #1 site for belt diagrams.

What engine does your 2500 HD have? Is it a 6.6 diesel, a 6.0 gas, or an 8.1 gas engine? If it's a gas engine, the A/C compressor belt may have snapped (common). The gas engines used a separate, smaller belt to drive the compressor, while the larger serpentine belt runs the rest of the accessories. Diesel engines only have one belt that runs all accessories, including the A/C compressor.

Light switch faulty looks like,

Dealer item

disconect the reverse light switch wires from the gearbox & bridge. If the lights come on it is a faulty switch.

fuel injection pump is failin or has issues--getta haynes manual for pro car maintenance

if i remember right its under the hood on the left side. should be a big black box mounted on the firewall. let me know if thats it.

Remove belt remove center bolt,remove pully install new pully install bolt and tighten.Re-install belt.

mo me it sounds like low fuel volume i would check my lift pump