[AT] tractor hauler a pain to install headlights.

[bradloomis at charter.net]

My VW DRLs are separate bulbs located under the headlights. They turn off
when the headlamps are on. And are a PITA to change. 

-----Original Message-----

I think there is a bit of confusion in regards to the auto light function
and the DRLs.

Many DRL systems do not turn on all of the lights. They only activate the
headlamps at reduced output. There are some that turn on all the lights but
they are not the most common.

The automatic lights usually have a sensor on the dash that detects the
exterior light level and turns on all of the lights once the light is below
a set level, just as if a human turned the switch.

I have seen those get fooled though, usually in bad weather where the light
gets reflected back to the sensor by for or heavy rain or snow. 
The backscatter is enough that it exceeds the threshold and the system
switches back to the DRLs.