Truck is Canadian 2011 XLT 4x4
How does the DRL circuit deliver power to the bulb for dim DRL operation? Is this reduced voltage or pulsed voltage?
Can the halogen bulb be replaced with LED?

Thanks!

 

It should just be regular headlight low beam for DRL, same low beam with Main light switch on

So any "recommended" replacement headlights will work fine

The DRL is in the Smart Junction Box(SJB) behind the passenger kick panel, cab fuse box is there as well
SJB is the "Body Computer" it runs all the cab electrics

Each low beam head light has its own fuse, power is supplied to those 2 fuses by the SJB when DRL module is activated

The Main light switch powers those 2 fuses when its on, the power runs thru the multi-function switch and then to the low beam fuses, the SJB detects the power coming from Main Light switch and turns off DRL at that time

The Main light switch has power all the time so key on or off doesn't matter
DRL will only power low beams with key on and E-Brake OFF, if you press e-brake pedal down, even a little DRL should turn off the low beams and Brake light should come on

 

No, does not work that way.
If the headlights switch is OFF or in P-Light position, ignition is ON (engine running) when the P-Brake is released the low beam bulbs illuminate at about 70% normal brightness. If I turn the headlight switch to the headlights on position the low beams get brighter.

What I am asking is how is the dimmed 70% brightness accomplished? Reduced voltage, or pulsed voltage?

Thanks!

 

There is no voltage regulator in the circuit, so if there is a voltage drop it would have to be PWM, pulsed voltage

EDIT: found a diagram that shows 2011 DRL driver with PWM out to low beam head lights, so it does lower voltage, only reason for PWM

 

PWM = Pulse Width Modulation so it isn't a voltage reduction, it is a pulse.

I got my hands on a Tektronix 485 O'scope and displayed the signal, a rectangular wave, 0-10 volts, 6ms on 3ms off, Low beam is steady 10 volts DC. Switch to high just lights the other filament, no change in voltage to low beam.
Just what will I do with this information now that I have it I do not know, but I shared it here.

 

Thanks

Yes, PWM lowers voltage, usually the Ground side is pulsed, like for the IAC Valv, EGR solenoid, and EVAP solenoid, PWM for these is used because it can vary the voltage, for the headlights it looks like a constant but lower voltage