Would it be easier to gut most of the truck out and swap in most of the explorer parts? i.e take the fuel tank from the explorer since i already have it. Also whats notoriously hard about using the explorer EFI compared to the mustang?
That sounds like you are considering the same path that betch was talking about and that I've tried once before. Attempting to swap in as much of the Explorer parts and wiring as possible. If the Ranger is mostly intact, I would not do that. You are just asking for too much trouble and work to replace things that are perfectly functioning. Read the posts in that other thread to find out more about my thoughts on that, I'm not going to retype it when the other is still on the first page of this section.
The Explorer tank probably won't fit the Ranger right, the frames and floors are pretty different. Even if it did, you'd have to run custom fuel lines.You could possibly take the fuel pump itself out of the Explorer and install on the Ranger sending unit,other than that I think I roughly covered connecting the fuel in my last post.
Explorer vs Mustang EFI...
What makes the Explorer hard is complexity. That EFI system is a lot more integrated into the body harness and other systems on the truck. If we're talking about the PCM itself the Explorer uses a 104 pin ECU for control, the mustang uses a 60 pin ECU. That means potential for an additional 44 circuits to make the Explorer run and a bunch of those are used. Also the Explorer EFI system has a 42 pin connector between it and the chassis harness, and most of those connectons are used to pass some signal or data. The Mustang EFI system on the other hand ios practically a standalone system from the factory. It only needs a few wires to make it run, really not much more than a carbureted engine I think, and maybe a few extra connections for gauges and warning lights but they aren't necessary. Heck the Mustang might use the same style ECU as your truck, so once you find the right wires, you might be able to connect to the same locations as what you are removing.
One of those conections into the body harness is the previously mentioned PATS system. The tech articles pretty well cover how to overcome that, but the Mustang EFI doesn't have to deal with it at all.
It may not matter since you are going manual transmission, but the 99 Explorer gets it's vehicle speed information from a sensor in the rear axle after it passes through the ABS box. You won't have either the sensor or the abs module. The sensor would be easy to get with an axle swap, but you do not want to try retrofitting the Explorer's ABS. My understanding is that both are required because the signal from the axle gets modified by the ABS module. Might not matter since you are going manual, I don't know if that signal affects the engine, or just automatic transmission shifting. Mustang EFI needs none of this, it just runs off engine speeds.
Mustang manual transmission ECUs are fairly common. Explorer manual transmission ECUs are nonexistant for the 5.0L and will require tuning to remove it.
Upgrade parts that work with the Mustang EFI are much more common. Tuners that work with the Mustangs also seem to be more common than for the explorer.
There are probably some other things I wanted to say, but I'm getting a headache and can't remember them right now. Also need to go get the shed closed up before it gets dark.