2003 4x2 Lariat Supercab

Does the on/off function for the underhood light come from the bulb itself or the base, perhaps a mercury switch? I’m thinking about adding more lighting and want to have them work the same way.

thanks!

 

mercury switch in the socket. I changed my bulb to led

 

Just go with the LED. Amazon has 4 packs of 1200 Lumen 912/921 for $10. Going to get set and put 3 in cargo bed lights and 1 in engine compartment. I will give pics and update. Going to post the pics of the cab LED i just installed today, amazing light.
these look pretty good.