If you would like to create a "Custom Google" map, you may enter it here. You do not need to copy the entire code. Go into your Google account and into Your Maps section and click on the map you wish to use and Click on the EMBED link on your Google page above the top right of your map and and copy the needed info shown below.
Copy and paste the code into notepad, microsoft word or anywhere you can view the entire code you have copied and select only the part of code below highlighted in red and copy that for your Custom Map field(your code will vary a little).
Once you paste the code in red into your Custom Map field the system will display your custom Google map.