Does anyone know about 2003 grid intake heater how do I know if it works or can I test it somehow

 

You would know when it's ON.
The would be a 2 volts drop and hence lights dim.

You can test it by jumping 12V to the positive side of the heater relay coil and then feel the heat from the heater.
Just make sure you don't jump 12V to the ground side.firework!

There were two grid heaters/relays on your truck.