I know with mine, it appeared that all were lit up all the time. When on low, the low filiament of all four bulbs will be on, and the high filaments off. When on high beam, all four high filaments will be on and all four lows off. UNLESS you have a brite box. Its sometimes hard to tell.
Craig
Try this. Pull your truck up against the house, a building, etc. Turn the headlights on. Pull the stick back and click on the high beams. With your RIGHT hand, click the stick back, then with your LEFT hand turn the headlight switch OFF. You should see some of the beams dissappear. Then let go of the stick. If it goes off then. You're good to go.
Craig
Now that you mention it, I'm not sure. The improvement was so dramatic over the standard lights I just assumed that all 8 had to be burning when in high beam mode, but I could be very wrong on this. I'll have to check. I used the SUV harness and nothing else, so whatever that setup yields is what i have.