Did this on my first project Mav 20 years ago. Had to draw up a vehicle diagram for a body electrical course. Mine had blinking side markers that alternate flash with the front bulb. Worked perfect on my Mav. Now I just have to remember what I did. It wasnt hard that much I remember.
The way I mentioned is the way it is on all the old fords with blinking marker lights. The reson the turn signal won't illuminate with the parking lights on is because the markers have a lower wattage bulb. (the whole path of least resistance thing) the only reson I even investigated this was because when I was 19 I had a 1974 ford van and was trying to find out why when I hit the brakes the side markers would go out. turns out that was the way it was supose to be.
Cool, thanks! I did a quick circuit diagram, and it makes sense. I'm still not convinced that providing a ground through another bulb's filament does not make it illuminate. I have a feeling that the bulbs do indeed light alittle, but since the other bulb is so bright, it does not matter.
Go to the autoparts store and buy a 1156 bulb and a 194 bulb. Now conect them in series to a 12v battery and see what happens.
Actually, I solved the circuit without spending any money: Vdrop_1156 = 1.85V Vdrop_194 = 10.15V So there is a voltage drop across the t/s, but it is not enough to illuminate it. This only works because of filament type bulbs. Convert to LED's and you are hosed. Thanks for the help Clint!