LED headlight lamps

[dwarrenk]

Here is a puzzle. I bought 6 Volt LED headlight bulbs for my 1930 Model A pickup. I replaced the passenger side with the new LED Bulb... it worked (it was much brighter) Then, when I removed the incandescent bulb on the drivers side... the passenger light went out. I then installed the LED bulb on the drivers side headlight. Neither bulb would light up. I installed the old incandescent bulb back in the drivers side headlight, both lights worked, the LED Bulb on the passenger side & the incandescent bulb on the drivers side. Why would the passenger side bulb only work when the drivers side had the incandescent bulb installed? I replaced the 4 taillight bulbs with LED bulbs... they all worked. (again much brighter).... another question (I'm a Model A newbie) on the headlights, there is the high/Low beam bulb in the middle, what is the bulb below that? Parking light? No matter what position the switch is in, these bottom bulbs will not come on. Yet another question concerning the taillights. There is a top bulb with a larger lens surface area & a bottom bulb. The way I got the pickup is the top is the running lights & bottom is the stop lights... is this correctly wired?