CORS: Accessing ssl endpoint from non ssl site

I'm trying to access my API endpoint (https) from a http:// site.
In my PHP Application i set the header to
header('Access-Control-Allow-Origin: *');

The response contains it. Nevertheless the following error occurs if i try to call the endpoint via AJAX:
ERR_SSL_PROTOCOL_ERROR

The cert seems to be valid. Can i disable the checking somehow?
It should be safe to access SSL content from an non SSL site. Correct?

The proper solution is to fix your certificate issue but if that is not feasible then you can use your HTTP server as a proxy to fetch HTTPS data via PHP's cURL:
HTTP AJAX call
$.ajax({
    url: 'http://www.example.com/call_api.php',
    success: function(data){
console.log(data);
    }
});

HTTP call_api.php
<?php
$ch = curl_init();

curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE); // return response as a string
curl_setopt($ch, CURLOPT_URL, 'https://www.example2.com/api_file.php');
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);

$result = curl_exec($ch);

if(curl_getinfo($ch, CURLINFO_HTTP_CODE) === 200)
{
    echo $result;
}

HTTPS api_file.php
<?php
// some database stuff returning JSON or whatever
echo json_encode($db_rows);