test to find the wire that turns on the fogs, and wire it up to the ignition on position.
But I am sure there is a much better method involving relays and or fuses.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.