How to make an ajax call to a php function with parameters in functions.php file WordPress

I am trying to make a call to a php function that I have added to my functions.php file in WordPress. I am able to execute the code without parameters but not sure how modify my function and ajax call to accept my posted data.

Within the functions.php file in WordPress this my code:

add_action('wp_ajax_get_parts', 'get_parts');
add_action('wp_ajax_nopriv_get_parts', 'get_parts');

function get_parts()
{
       //DOING STUFF

        echo $output;

        wp_reset_postdata();

        die();
}

And this is my ajax call:

$.post("/wp-admin/admin-ajax.php", {'action':'get_parts'}, function(data, status){
    //DOING STUFF...
});

I want to change my php function to accept two parameters (partnumber and zipcode):

function get_parts($partnumber, $zipcode)

And within my ajax call I would like to pass two values from textboxes (Example of what i have):

$.post("/wp-admin/admin-ajax.php", {'action':'get_parts', 'partnumber' : $("#searchtbx").val(), 'zipcode' : $("#ziptbx").val()},
function(data, status){

});

As of right now I am able to call the function and get data. How do I pass two parameters (partnumber and zipcode) to php function?