There is only one wire that goes to the cluster and the cluster is all one piece. As I have said before, if I knew what year it was and if I had the part, I would sell it to you.
The cluster retains the memory for the mileage and the engine hours in the prom in the cluster. All you need to do is find a cluster with the amount of miles on it that you wish to have. Plug it in and it will work.
I would check all the fuses with a ohm meter, one at a time. But fuses are a all or nothing type of thing. Either they work or they burn out. When they burn out, you can bang on the dash all you want and it is not going to come back on.
You have a electric box under the hood that has the general electrical fuses, lights, turn signals, etc and you have a second fuse panel inside of the truck on the drivers or passengers side under a removeable panel. About the only thing you can do is take them out and make sure that nothing is corroded and put them back in - one at a time.
Check the ignition key and look on her key ring to see if she is one of those stupid women that has a bunch of junk hanging off the end of the key ring.
If she has a bunch of junk, be prepared somewhere down the road to spend a lot of money to replace the ignition cylinder.
Many time when I see problems like yours, it is associated with the key and the junk on the key ring.