This is a very simple circuit to test with a test light....
Take your test light and attach it across your battery terminals and note the brightness of the light.....
Now with the test light still attached to the negative cable, turn low beams on.....probe the terminal in the socket with the tan wire going to it....test light should be bright.......now turn on high beams and probe the terminal with the lt green wire to it, and it should be bright.....if neither is bright, repeat the test by shaving the outer layer of insulation of each of the wires going into the socket, about 3" back......if now bright, replace the socket.....
If the first test shows the test light bright at the socket contacts, now move the test light clip from the neg term of battery to the pos terminal, and probe the terminal in the socket that goes to the black wire...if the test light is bright, like the other two terminals, bad bulb.....if the test light does not light, shave the black wire back 3 ", and probe, if it lights, need socket....if it doesn't, you have an open ground wire......easiest fix is to run a redundant ground wire to the black wire....