what am I doing wrong 

{
"Settings": {
"CategoryDefaultStack": {
"Ammunition": 1000,
"Attire": 0,
"Common": 1000,
"Component": 10000,
"Construction": 0,
"Food": 0,
"Items": 0,
"Medical": 1000,
"Misc": 0,
"Resources": 10000,
"Tools": 0,
"Traps": 0,
"Weapon": 0
},
"DefaultStack": 0,
"StackHealthItems": true
}
}

Nothing appears wrong with the config from a glance. What kind of issue are you having? 

If you're having the issue with stack sizes not being set to 10,000 for items in the respected categories, you have to run the "/stackall default" command to update the data file (or update it yourself in oxide/data/stacksizecontroller.json). 

So the issue I had today was even that I had this all setup in the config area I also had to go into oxide/data and set each iteam. Some never took the settings untill I went to the list and edited it all by hand. 

Did you reload the plugin after saving the data file?