There is a schematic in the back of the Haynes manual. My alternator isn't working on my Mustang, the the problem is complicated. The big wire charges the system, and that's pretty obvious. There are one or two fusable links on this main wire before it goes into the junction or to the battery. Not exactly sure how it is on a 95' F150. On the Mustang it junctions on the side of the fuse box before going to the battery. Check for wire continuity to make sure those fusable links haven't blown. The little white wire that goes back to the alternator controls the field current. I assume you had the alternator tested on a bench, which means the field current wire is working. The other two wires are usually yellow and green. The yellow one is usually slight larger, if the colors are not exact. Anyway, the yellow one has 12 volt power from the main fuse box in the engine compartment. That wire should have 12V power regardless of key position. If you aren't getting 12V power to that wire, check the alternator fuse in the main fuse box.
Now the green wire is the real MF and far more complicated than the rest of the wiring. The green wire goes to a circuit that travels through the instrument cluster, and the charge fail light. This is the circuit that is messed up on my Mustang. The circuit starts at the ignition switch which provides 12V power to the circuit. The power travels through one of the circuits in the instrument cluster, and parralel circuited through the charge fail light, and a resistor that is there in case the charge fail lightbulb blows. It then travels through the instrument cluster back into the harness and too the alternator. The circuit provides power to the alternator to tell it to turn on. Once the alternator is on, the positive voltage should be equal on both sids of the charge fail light and therefore it won't illuminate. If the Alternator fails, then the voltage will drop to 0 on the alternator side, and power will travel to the alternator illuminating the bulb. It also works for an over voltage condition on the alternator with electricity flowing the other way. Anyway. With the key in the on position, there should be about half battery voltage at the green wire due to the resistor and light bulb. So, about 6 volts at the green wire.
There is some sort of short in my Mustang and it keeps frying the circuit in the instrument cluster, causing the alternator to not turn on.