Wow! You may be making this more complicated than it is. You may have done so already but it doesn’t hurt to take a few steps back. Firstly there are countless places in the circuit that can cause a fuse to blow but only one reason(current exceeds capacity of the fuse). An overload is possible if you add loads to the circuit. Every part of the circuit has resistance including wires, connectors, relays, and loads. if a load has a rated resistance that requires 12 volts to operate, it may still operate at a lower voltage but it will draw more current. However, loads are typically not the weak link in a circuit. They function, don’t function, or function poorly. The weak links are all the connections in the circuit susceptible to physical damage. eg. pinched/broken wires, corrosion, or loose terminals. You don’t need a wiring diagram at this point but you should have a voltmeter, small wire brush, flash light, wrench, and screwdriver. Keep in mind the age of the wires, insulation, and number of times the harness has been pushed, poked, and prodded. All areas have been subject to corrosion and some more than others. The prerequisite for corrosion is moisture. All of these cars have been subject to humidity and many have had leaks. Multi stranded wires soak up any and all moisture like a sponge so areas that have been exposed to it are likely to have been exposed to water damage are places to focus. Short of rebuilding and replacing every part of the circuit, focus on the most likely places for resistance to occur. Always start at the power source to make sure you have 12.5-12.7 volts(loads off/engine off). Then observe exposed areas looking for signs of corrosion, loose connections, and broken wires, measuring voltage at every point that’s accessible. Don’t cut into or pierce insulation to get a measurement. If nothing’s obvious extend your view starting at the fuse block and inspect connection points, connectors, terminals, and wires, front to back. Next pull the instrument cluster and inspect the primary ground point on the column mount or chassis(many brown wires soldered and crimped into a few large ring terminals, fastened to the ground point). While you are there clean up the terminals and ground point with a small wire brush until they’re shiny. You’ll need to remove these terminals and clean both the hard point on the chassis and the terminal surface in contact with it. It does no good to leave it in place and clean only the top. If terminals are stacked, then it’s important to clean both sides. Finish up with a VERY light coat of your choice of electrical/corrosion coating or silicone dielectric then torque the fastener. Next check the connector to the instrument cluster for corrosion and the dimmer switch resistor. If the female connector is very corroded, cleaning it up is damn near impossible but electrical contact cleaner and compressed air might help. The male pins on the board can be cleaned up but be very gentle. A pencil eraser or small piece of 800 grit on a toothpick… it’s a tedious job.
Now you can remove kick panels and inspect the harness anywhere it contacts a hard point ( places wires are susceptible to damage from tears of vibration). Look for areas where the harness has been disturbed or altered by yourself or PO’s). If a problem presents after any job no matter how small or seemingly unrelated, 9 times out of ten it was caused or compounded during that process. If you’ve done a thorough job of the previous steps it’s time to roll up your sleeves a bit higher but 75% of the time you’ve already encountered the culprit before diving into more complex or harder to reach points in the circuit.