Been blowing one 60a fuse over and over

What was that fuse for? There's a diagram pasted under the fuse box cover.

I show two ignition fuses and both are 40 amp. I've never seen a 60 amp fuse and none are shown for a '99.

I DO show four large fuses in one row and six in one row next to that first row. Describe for me which fuse is blowing. Is it the one at the end of the row of four, closest to the bolted-in fuse, or is it the second one away?

Also, if you're going to put another fuse in, a real good clue can be found by not installing it until after you turn the ignition switch to "run". If the fuse doesn't blow until you try to crank th engine, that leads us in a different direction than if it blows before you even turn the ignition switch on.

What I'm not doing a good job of saying is if you put the new fuse in first, THEN turn on the ignition switch, the automatic shutdown (ASD) relay is going to turn on for one second, then turn back off until you crank the engine. If you wait for that one second, then put the fuse in while the relay is off, and the fuse doesn't blow, we'll know the problem is on that circuit.

You can also remove the ASD relay, then see if the fuse blows. If it never does, the short is on that line. First look at the wiring for the four oxygen sensors. If the harness fell down onto hot exhaust parts and melted, the heater wire could be grounding out. That is fed from the ASD relay. If that looks okay, have a 12 volt light bulb and a pair of small jumper wires handy for the next test.

Rather than popping lots of fuses, remove that one, fuse 9, and connect a pair of jumper wires to the terminals in the fuse box. I think you can clip right onto them. If not, install a pair of crimp-type terminals that you can connect the jumper wires to. Connect the other end of the wires to a 12 volt bulb. Since this is such a high-current circuit, a head light bulb is the best choice but a brake light bulb might work too.

When the bulb is full brightness, the circuit is powered up and the short is present. The idea now is to see what makes the bulb bright and what you can do to make it go out or dim. Unplug the starter relay if the bulb only gets bright during cranking attempts.

If the bulb gets bright only when the ignition switch is turned to "run", one at a time unplug fuses 2, 3, 7, 18, and circuit breaker 20 inside the truck. I doubt you're going to get that far because a short on any of those lines should blow those smaller fuses, not a bigger one under the hood. The only exception is a short before the wires get to those fuses, meaning a grounded wire in the steering column going to the ignition switch.

All right. One in a row! Happy to read it's solved.