Halogen fog light bulbs

[NutmegCT]

Brain failure again.

I've got two IPF 804D 12 volt fog lights, similar to:

Each has two leads: red and blue.

When powered up, both lights are very dim. I thought at first it was due to age (bulbs, not me).

But then I noticed there are two bulbs in each light. A small one in the upper left corner (barely visible in the photo), and the large bulb in the center. The small one seems a bit black inside, but does light. The large one never comes on.

Would anyone know why there are two bulbs in each light?

Thanks.
Tom M.

 

[TR3driver]

I don't know, but I would guess its something similar to a "city light". Basically just a small light for use when the big one is not appropriate.

I'll also guess that the two wires are both hots, and the housing must be grounded.

 

[NutmegCT]

Thanks Randall. Makes sense, as the red wire is smaller gauge than the blue wire. I'd never heard of fog lamps having a "running light" built in.

Test: just tried 12 v at the bracket (ground) and the red wire. Small bulb came on. Tried same at bracket and blue wire. Center bulb came on nice and bright.

Learn something new every day.

Tom M.

 

[JPSmit]

My father's DKW had what I think was called a "Parking Light" dim light on the road side that could be illuminated at night when parked on the road.