Well, the pictures show the wiring under the hood has been modified. So we need to figure out what modification was done wrong. Don't worry, it shouldn't be that hard. We just need to follow the wires.
Can you follow the diagrams in post 36 & 37?
If so, do you see how the headlights couldn't effect the ammeter in the original layout?
If you have trouble reading or following the diagram, just ask whatever doesn't make sense.