Pat in Texas

Thanks. Ground problem is certainly a possibility but my main question is still unanswered, where can I find electrical diagrams online that don’t require a fee?

I have a 2002 Silverado 1500, 5.3, 280k miles that suddenly developed a problem. The A/C fan & controls died, the PRND display went dark & the battery symbol in the message center came on. The PRND display shows up with the key in first position off lock, but goes out @ the next & when running. With no key in, pressing the reset button shows mileage. Battery voltage shows 13.8 when running. I assume there is a common point in these circuits but I haven’t been able to find the correct wiring diagrams. Any pointers? I’m well acquainted with electrical & electronics troubleshooting & design, just not familiar with the specifics of this vehicle. thanks for your help. Peace, Pat