Maybe I can contribute something - unless itis already commonly known or unless more experienced colleagues would say it is a true nonsense... But maybe it is useful for some of the colleagues from Europe.
In some European countries we have to use day running lights (DRL). For older cars it means just to have headlights always on or installing some sort of additional lights (often LED). I believe our cars are not designed for permanent driving with headlights on. Moreover all the bulbs in the dash are also permenently on, which causes their premature wear and replacement necessity.
You can install additional foglights - ok. But, according to a lot of country regulations those are supposed to be on only together with headlights on. Also: not everybody wants or likes them.
What I did: I have the Euro headlights with foglights. I hooked the power supply to the foglights to the headlights switch (that is where they are normally supplied with power, but only after headlights are switched on), but it goes through a correct switch in the tray (I used my rear window heater switch for that as I do not have the proper glass anyway) and a relay. So the foglights can now be independent, you switch them on when you start the car and they act as DRL. Alternaor, installation is much less loaded, the bulbs in the dash are not on all the time. No need for any additional lights.
If you come across a regular switch - you use regular relay, if the switch is impulse (that is what you may get from Mercedes these days) - you use impulse relay.
Just a bit easier life...
