Go to AutoZone or similar and ask them to do a full load test on your vehicle's charging system. It should detect any bad diodes.

Moving the head unit ground to the battery: as long as you used an ultra low resistance cable it should be fine. Otherwise you may be adding to the ground loop issue.

 

ah thats kind of what i was assuming, i'm fairly confident the issue is the 2ga ground that goes from the transmission to the chassis, the resistance reading was really high on it and its covered in an oil vapor, guess thats an issue for another day. i got a new one on order from rockauto for $27 shipped. i dont know if i'm going to keep the HU ground long term, but i did use 16 or 18 ga wire. the HU isnt powering the speakers so i dont think it would be drawing too much power.

 

What are you using for the ground wire?
Copper clad aluminum (CCA) or Oxygen free copper (OFC)?
The former only has 60% of the conductivity of the latter.

Should Also be using copper terminal hardware.