The E mark on the lens will tell you what they are. Above the E11 mark that means it's a UK spec lamp, it will have a square with B if it's a front fog lamp or HR if it's a halogen main beam of any kind (driving, spot, etc.). It may also say PL for plastic lens if it has one.
Nev suggests that wiring them into the main beam is convenient for spot lamps, it is more than that it's the law! Any auxiliary main beam lamps must be switched off by the dip switch. As said above front fogs should be wired so that they can be used when the weather is bad. If they are wired so they can be on independantly of the dipped lamps, they must be positioned on the vehicle as dipped lamps would be (within 400mm of the outside edge etc.). If they have been fitted in the middle, and are fog lamps, you should wire them so that they can only be on while the main light switch is on and then have their own switch as well. It's also a good idea to wire them so they can only be on while the rear fog is on, as this should be on long before front fogs. When fitting any extra lamps, relays and new circuits must be added as none of the original wiring can cope (except on MPi cars that are pre-wired for additional lamps).
Edited by Dan, 11 May 2012 - 10:10 AM.