OK so that pdf is a bit blurry but on pg 28 it shows 14 v power line go first to a few transistors in the power regulation circuit , anything past those will not read with a meter due to the semi conductors . It looks like 3 connections are coming in on that plug , the lower one heads off and goes to a few collectors on transistors just like the diagram . How does this unit switch from battery to wall power ? The digram on pg 28 it ' s blurry but it looks like there is connection 1 and that ' s negative . Then a connection 2 that is battery power with an arrow that ' s pointing to pin 3 and that ' s main power . The 3 connections on the page 28 diagram are the 3 lines coming through that plug so the 3 should be battery , main power , ground . That arrow between pins 2 and 3 to me suggest that maybe there is something in that plug that transfers power from the batteries to the main line when nothing is in the socket . Maybe that is broken . So you would read battery power from battery connection 2 to ground connection 1 but you should be able to read power on connection 3 to connection 1 .