Issues with 2000 sterling truck

Having issues with a 2000 sterling water truck. The truck has a slight draw on the electrical system. Cleaned all connections but found during the manufacturing at the truck they just cut the trailer harness off and did not put a dead connector at the end(repaired already), Also, the truck can run put if you let truck stay at a certain idle for to long the eng light will flash real fast then die. I found that if you accelerate the engine it will go out. So I was thinking oil pressure put the gauge is reading 40psi at 1800rpm's. (sensor??) Performed the old fashion blink light retrieval off of the engine light for fault codes and had alot of codes 46, 47, 21, 51,38,36. 21, 51, are dealing with the battery system. 46 is oil pressure, 47 is idle shut down(engine protect),



What I am asking does anyone have the schematics for this truck?? Or any suggestions??