1. When you place the negative lead of the multimeter to the negitave terminal on the battery (or a good ground) and the positive lead of the multimeter the positive side of the headlight terminal WITH the lamp inserted you get 12V
2. When you place the negative lead of the multimeter to the negitave terminal on the battery (or a good ground) and the positive lead of the multimeter the negitive side of the headlight terminal WITH the lamp inserted you get 12V
Assuming this is correct... you do not have a ground to the headlight terminal.
