Instrument/dash panel fuse light keeps blowing out

I can get you started. A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a twelve volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it is not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.

I am not familiar enough with Toyota radios to know for sure what are the best suspects, so my recommendation is to start by unplugging the radio, then see if the test bulb stays dim or a new fuse does not blow. Typically original radios have a connection to the tail lamp circuit to tell the display to dim when you turn on the lights, and another connection to the dash light circuit to tell the display how much to dim. There may be other lights on the dash light circuit for the heater controls and for floor shifters, when used. Also, look if you have lights in the power window and/or power lock switches, and if you do, do those adjust with the dash lights?

Spade terminals are generic parts that many people have laying around. They are simply used to give you something to attach the jumper wires to. It does not make sense to buy a pack if you are never going to use them again, but you can find them at any hardware store, auto parts store, Walmart, and places like that. You can also just stuff wires into the fuse's socket. In fact, if you use a newer-style 3157 brake light bulb, it has wire terminals that lend themselves to hooking wires to that you can plug into the fuse box.

The type of clip leads I use can be found at Harbor Freight Tools, and probably at any hardware store. They cost about three bucks for a dozen, as I recall. They come in blue, red, white, green, yellow, and black, and they're about 12" to 15" long, with a spring-loaded clip on each end.

If you really want to get creative, you can grind away part of the plastic on a blown fuse to expose just enough of each terminal so you can solder a wire to each one. Use an old bulb socket, (zillions of them at any salvage yard), and solder its wires to the old fuse. Now you can just plug in that fuse and pop a bulb into the socket. I made one like this with wires long enough that I can hang it from the rear-view mirror so I can see it easily from in back of the vehicle.

Also, you can grind the plastic away from the blown fuse so you can clip a pair of clip leads to those terminals. That way you will not have to buy a box of terminals.

If there had been little lights in the lock and window switches, there would be wires feeding those lights that ran through the door hinges. Those wires often break or fray and create shorts and/or dead circuits. Since you do not have those, that just eliminates one possible place to look for the cause of this problem.