I'm posting up a PDF file that you can download, this is the diagram, I'm going to do this in steps so I don't confuse you. It might be a little hard to read the colors on the diagram but I'll help you out with that.
Find the ignition switch and make sure that you have battery voltage on the red wire leading to the ignition switch, if you follow that back it will go into the electrical box, if you don't have battery voltage (12 volts) on that red wire to the switch stop right there and let me know.
So you have a white wire and a red wire on the "in" side of the switch, remember red should have battery voltage regardless key on or off. Now if voltage is there then with key on you will find a red/white r/w wire out of the switch, measure voltage on the r/w wire, that goes up to a "joint" connector, if you look on the diagram you'll see that the r/w wire goes into that connector then a bunch of wires (r/w) and an orange wire, this is basically what splits off all the power to all the various components that require 12 to power them up. You need to make sure that you have power (battery voltage) on every single wire (with the key on) in that joint connector.
So turn your volt meter to VDC so you can measure the voltage at the battery, this will be your baseline, then (-) black meter to good ground (battery) and then the positive (+) lead to check all your voltages that I gave you earlier. Easy was to test the voltage on the individual wires is get yourself a safety pin and poke it threw the vinyl sheathing on the wire.
Let me know your results, make sure you write them down as you are performing your tests.