Ignition fuse keeps blowing

Yes. Unfortunately, throwing random parts at the problem is the least effective and most expensive way to solve this. A relay is just an electrically operated switch. While it is possible, it is extremely rare for one to short. Instead, they can switch a short onto a circuit that allows excessive current to flow and the fuse to blow. Replacing the relay doesn't solve the problem or make it go away.

The next concern is your comment about having to replace a ten-amp fuse to start the engine. That implies the engine does start and run at times, meaning the problem acts up intermittently. Those are the most frustrating problems for mechanics to find because very often we can't be sure we found the solution until you come back and tell us it's still acting up. I do have a trick that can help with this.

The first thing we need to do is identify exactly which fuse is blowing. See if you can identify the fuse from these drawings. The first five are for the under-hood fuse box. The last five are for the fuse box at the left end of the instrument panel.

How often does this fuse blow? Is there anything you can do to cause it to blow?

I found this diagram showing some of what this fuse feeds. The main thing is the neutral safety switch in the starter circuit. I also found a reference to it going to the instrument cluster, but I haven't found which circuit it feeds.

With such little to go on so far, the best place to start is by inspecting the wiring harness going down to the transmission. Look for the black wrap chewed away in one area, or the harness has been rubbing against something and worn through the insulation of some wires.

Next, check under the dash in the area the clutch pedal would be if you had a manual transmission. Very often just one wire harness is made for multiple applications, then unused items will either be left with an open connector or there can be a jumper connector installed. Look for a plug hanging down with a bare wire that is able to rub against something metal.

The next step is the trick I mentioned earlier. That is to replace the blown fuse with a light bulb. When the short occurs, the bulb will be full, normal brightness and hot, so be careful what it's laying against. It will also give a nice indication of current flow through that circuit, and it avoids wasting a lot of fuses. I drew up these drawings to explain the procedure. A common 3157 brake light bulb should work fine for this. It will allow a maximum of one amp of current to flow when the short is present. It is possible the circuit, or parts of it, will not function properly due to the bulb's resistance, but it will allow you to work in the area.

With the bulb in place, move or wiggle wire harnesses, turn on various switches, or do anything else that might make the short occur. When it does, the bulb will become bright. If you're lucky enough to get it to stay that way, very gently move things around until it dims. That will tell you you're in the area of the short. I've also found sheet metal screws run through wiring harnesses by banging on the body with a rubber hammer.

Let me know how you make out with this procedure.

Dandy. Very happy to hear you found it. Please post an update when this is repaired.