I don't know of a schematic, but you can figure out the continuity of each terminal with a multimeter.
Here is how mine is wired. There are three different terminals - red, yellow, black. Two connections per terminal, top and bottom, for six total connections to three terminals. The top and bottom rows are the same terminal. The red terminal is one pole or line, yellow is ground, and black is another pole or line. Since this inverter is a 120VAC high frequency inverter, it does not provide 240VAC, so you don't get the traditional four terminal connections - black line1, white neutral, red line2, green ground. Instead you get a similar configuration where the sum of the two poles is 120VAC instead of 240VAC. You can think of this inverter as two inverters running in parallel just like any two 120VAC high frequency inverter do when you put them into a parallel configuration for 240VAC. I guess you could also think of this inverter as using split - split phase or parallel-half-split-phase, or whatever you want to call it. Its just two separate phases running in parallel to each other at 60VAC each. The voltage measured across the two poles is 120VAC, just like the sum of two parallel 120VAC inverters is 240VAC. Why in the world would they do such a weird thing? Its not weird. It's the way every state of the art (high frequency) inverter works when paralleling. With this inverter they simply leveraged the same design but for 60VAC instead, and the microcontroller and communications are encapsulated inside the box. On the outside you get the expected 120VAC.
How can you verify everything I have said?
Yellow Terminal (Ground)
With the battery disconnected from the inverter, set your multimeter in continuity mode if it has one, or if it doesn't put it into resistance mode (ohms) to test for resistance. Then touch one meter lead to the yellow center terminal and the second meter lead to one of the screws on the inverter chassis. If your inverter is like mine, then you will hear the buzzer and see the light that there is continuity between the yellow terminal and the chassis, or if you are using the resistance setting, you will see the resistance go to zero. Now touch either lead to each of the ground holes in the outlets. They will all show continuity with the chassis, the yellow terminal and each other. This means that both the yellow terminal and the inverter chassis are connected. This means they are ground. When you connect your appliance's green ground wire to the yellow terminal you are truly grounding your inverter and the yellow terminal to the appliance ground. If the appliance has been properly grounded, then you are also grounding it to the building's true single point to ground. Note that this also means that neutral or white of the appliance isn't tied to ground as in a standard residential black, white, green split phase configuration. If it were then there would be continuity between the yellow terminal and the black (or red) terminal and there isn't, because that would be a short in this design. This also means that if there is a ground fault (someone touches a live wire - either pole), then they should only experience 60VAC rather than 120VAC and there will be an imbalance between both poles causing the GFCI outlet to trip.
Red/Black Terminals (line 1, line2)
Now touch one of the meter leads to the red terminal and the other lead to the wider of the two slots in outlet A (the one most left). You should also see continuity. If you touch it to the same slot in outlet C (third one from left), the same thing happens. However it does not happen on outlet B or D. That means that they have alternated the connections for the left slot on the outlets between the red and black terminals. A and C are wired the same. B and D are wired the same but opposite of A and C. The left slot on A and C is red and the right slot on A and C is black. The left slot on B and D is black and the right slot on B and D is red.
Since we are talking about alternating current here the concept of polarity, really doesn't matter. So when you wire up your appliance you can connect the appliance's black wire or white wire to the red terminal, and the appliance white or black wire to the black terminal. Now you have the appliance's black and white wires connected and will have 120VAC to the appliance.
Here is a summary of wires to terminals:
green wire to yellow terminal
black or white wire to red terminal
white or black wire to black terminal
If you are concerned about AC polarity (what?), outlets A and C are the same, and B and D are the same but opposite. The rule is that you always wire the wide blade to the neutral (white) and the narrow blade to hot (black). But since there isn't a neutral and there are two half hots, those rules don't apply. I have read a review where someone said that the factory miswired their inverter and got two of the outlets backward, so they rewired the terminals inside the inverter to 'fix' it. What this does to the inverter design though is uncertain. The inverters are by design wired this way to alternate the outlets. I don't know the reasoning behind it other than maybe it has some affect on balancing the load somehow over the two halves or something. That would only make sense though if we were running this inverter as a 60VAC split phase inverter. But we aren't, so there shouldn't be any way for one of the halves of the inverter to become more loaded than the other half like with paralleled 120VAC inverters. I'm not an inverter electrical engineer, I just pretend to be. Who knows how its designed and connected internally? Anyone? An alternative to rewiring the inverter with the terminals is to simply wire one external appliance to red and black and a second with black and red. This way you rewire them outside rather than inside without tampering. My opinion is to just use it as is and not fiddle around with it. Electrical engineers designed the inverter and I don't profess to know more about their schematic than them, especially since I haven't seen them. I really don't believe though that every inverter they make has the same two outlets miswired by mistake. Maybe I'm wrong, or maybe the assembler is just left handed or using a mirror half way through. Maybe it saves them 10 cents in wire because the right and left blades on every other outlet are next to each other.
So that's all there is to it.
