where whould i find the headlight switch in a bmw 316i compact

The hedlight switch is the one you use to turn the lights on/off.

You can just wire them to the clearance lamp by splicing into them. If you are not sure of wirings, it is best not to attempt them. Any mistakes an be costly.

i think i got it basicly i follow the wire from the main headlights cut into them wrap the led wire round them and tape it up properly yh?

That is correct but it would mean the lights that you are adding would only work with the headlight circuit.

You can have other alternatives such as having the lights turned on when the ignition switch is turned on, etc.