Old post but did you find any resolution?? I'm having the EXACT same issue. 1.3v remains on circuit after key is turned off the majority of the time. Seems to do it EVERY time after you throttle past idle.
I’m not certain of the fix BUT if u go to the fuse panel and pull the fuses 1@ a time and test the circuit u are getting the voltage to, at least you’ll find the circuit it’s powering..
My guess is a bad diode in the alternator..
Good luck
