That, young grasshopper, is totally a subjective question. I could be very easy, or very hard. Would depend on WHERE the problem is. If it's a cut wire, if you can find the wire, easy.
If it's the sending unit..... could be very hard. How hard is based on what tools you own and how good you are with a wrench. If you have a deep wallet, it could be as easy as a trip to the local machanic.
Welcome to the wonderful world of wrenching on an Explorer! Easier then most newer cars, got good room to work in. Rust is your biggest issue, some of those bolts just DON'T want to turn.
I have a decent tool set, and so far I haven't run into anything too hard, and I've wrenched on it every weekend for 4 months doing something. But I also work on/build cars for a hobby...so yeah, grain of salt...