Cat 3126 will not shut down

Ongoing issue port engine at times will not shut down. Have checked relay and fuel selinoid both appear ok. When at idle amp is +4 depressing stop increases to +6 when released drops to -6 and returns to +4

If I increase RPM and turn on crossover battery meter increases to +12 / 14 and motor will shut down after a few minuets . Cat is a year 2000 with 700 hrs. Port engine charges house Starbord charges cranking. Both are wired with preheat that turns off at 120F. Both engines run at 180F. Problem occurs mostly on short runs.

Apreciate any advise. Thank you