I am an electronics enthusiast and I am helping a friend decipher a wiring harness diagram for his vehicle. He sent me the attached image to help him figure out what wire goes to where, but both he and I have the question on what do the filled vs non-filled circles indicate. Any help on this would be greatly appreciated.
Wiring diagram legends are invaluable for detailed info. The best answer would be from factory service manuals. Sometimes someone posts them online in vehicle forums from either personal manuals, dealer techs, repair shops, etc. These would be hit or miss at best. Alternatives are buying service manuals, subscribing to Alldata.diy or Mitchell data for online access to factory service manuals. Some local libraries have free access to alldata.