how do daytime running lights work on 1995 S-10?

[dmjlambert]

I have a 1995 S-10 pickup base model. I think the daytime running lights work when the headlights are off but engine is running and they seem to be partial brightness. How is that partial brightness done? I am wondering if there is a module of some sort that sends a pulse width modulated signal to the lights, essentially making them blink on and off fast enough so a human eye can't see the blinking, or if there is a relay that puts the headlights in series with each other to cut the voltage in half, or some other method.

The reason I'm asking is the normal operation of the headlights is malfunctioning, they are very dim, and I would like to go to the module or relay and check the voltages there (where ever that is). I'm only getting about 6 V at the headlight when headlights are on, and about 3 V when headlights are off for daytime running lights.