How do i use my 400 Watt Power Inverter on my 2006 Jayco Class C?

you are correct. check the fuses on the converter itself, it could have some. mine does. .

And check the 12 volts that is going to the inverter to see if it getting any power.

If it is getting 12 v ,then the inverter could be shot. Which would happen easily if someone over loaded it. ( see if it has its own fuse on the unit itself) as i said.

A 400 is a very small (tiny) inverter.

I use mine in my boat and have a 1500 watt unit. Which is still a small inverter.

First see if are getting 12v to the unit and go from there.

A power inverter changes dc to ac you should have 400 watts of ac power with the switch in the on position

If there is at least 12 volts going to it.

relies upon on the battery. in spite of if this is a 12 volt battery; and rated for, say, 3 hundred chilly Cranking Amps, this is one hundred A/Hr, ten hours at a 10 amp drain. Your bulb is 20 watts, the performance of a smps is 80 5%, so as this is 20/.80 5 = 23.5 watts. 23.5 watts/12.6 volts= a million.86 Amps. properly under the ten A/Hr fee. ,12.6 volts x 100A = 1260 watts/23.5 watts = fifty 3.6 hours. 4-6 hours an afternoon it is going to attend to. maximum motor vehicle batteries are not made for this. A Marine, golfing cart, or different deep cycle battery will do it lots longer and final longer, too. EDIT: Batteries are rated in Ampere/Hours, no longer watt hours. EDIT: All change mode powers supplies run at approximately 80 5% performance, no count what output or load (until overloaded, of direction. Then they only close down.) I fixed ''em for 8 years, professionally.