Cat d6nxl akm 372. Battery indicator flashes all the time, but alternator still charging batteries. Code says it is bad negative ground some where. Where to start looking?
Check your main ground first off. Disconnect the cable at battery and master disconnect switch, if used. Then check the ground at starter also.
A schematic would trace back the power from alternator to find broken wire or defective component. Maybe Good Nige will help you. He has given hundreds of schematics, probably thousands. Simon C