Engine won't start, or even crank. Last thing was l left headlight switch in 'park' position a few days ago. My fault but thought modern vehicles had 'auto-off', especially since I don't recall seeing the parking lights after ignition switch was turned off and I was leaving the storage lot. Meter in the RV house showed about 10V on chassis battery. When attempted jump start, showed 12V but still absolutely no starter sound. Just clicking sound(s) from within the cab somewhere and lights on instrument panel flashing. Checked most fuses and breakers - no smoking gun. DEF is full, electrical disconnect is confirmed not disconnected. Tried replacing starter fuse with new. No change. Ideas? I really don't want to pay to have this heap towed again. Thanks in advance.