How to add navigation screen to mesh?

You need several things I think:

1. A reference to an ETK 800 gauges controller in your car's body Jbeam:
   
   Code:

   "controller": [
           ["fileName"],
           ["etkGauges", {"materialName": "@etk800_gauges_screen", "htmlPath": "local://local/vehicles/etk800/gauges_screen/gauges_screen.html"}],
       ],

2. A flexbody with a material named etk800_screen where the GPS would be, with a deformgroup, like this:
   
   Code:

   {"deformGroup":"display_break", "deformMaterialBase":"etk800_screen", "deformMaterialDamaged":"etk800_gauges_break"},
           ["etk800_screen", ["etk800_dash"]],
           {"deformGroup":""},

3. A definition in main.materials.json:
   
   Code:

   "etk800_screen" : {
       "name" : "etk800_screen",
       "class" : "Material",
       "persistentId" : "ed4c0c35-2305-4f49-9813-b2f4e088359b",
       "Stages" : [
         {
           "colorMap" : "@etk800_screen",
           "emissive" : true,
           "specularMap" : "vehicles/common/null.dds",
           "specularPower" : 32,
           "useAnisotropic" : true
         },
         {},
         {},
         {}
       ],
       "alphaRef" : 0,
       "mapTo" : "etk800_screen",
       "materialTag0" : "beamng",
       "materialTag1" : "vehicle",
       "translucentBlendOp" : "None"
     },
   

4. If you want the screen to break on crash, add this deformgroup to the interior beams:
   
   Code:

   {"deformGroup":"display_break","deformationTriggerRatio":0.05},

   And then you also need a new material:
   
   Code:

   "etk800_gauges_break" : {
       "name" : "etk800_gauges_break",
       "mapTo" : "etk800_gauges_break",
       "class" : "material",
       "Stages" : [
         {
           "diffuseColor" : [ 0, 0, 0, 1 ],
           "specular" : [ 0.5, 0.5, 0.5, 1 ],
           "specularPower" : 128
         },
         {},
         {},
         {}
       ],
       "translucentBlendOp" : "None"
     },
   

That's probably all unless I missed something. Do not change the name etk800 in these to anything else because that's defined in the LUA controller. It's a common controller so you don't have to copy any LUA from the ETK 800 files.