Tail fuse keeps blowing.

[CrankyOldMan]

As long as you're not breaking the connectors you're fine. ;) There's a black retaining lever thing that holds them in place and helps to pull them out.

Here's the layout of the junction block:

[tuppy]

Originally Posted by CrankyOldMan

Here's the layout of the junction block:

Hi, thanks again for your help. I found a complete copy of the 2007 Yaris wiring diagram online and after studying it a bit was able to work out which connectors on the junction box I needed.

After disconnecting 4A and 4B and inserting a new fuse, I could turn the headlight switch on without blowing the fuse (though the headlights didn't work of course). Then I tried with just 4A connected without issue, and again with just 4B connected, which left me very confused. So I connected both again and the fuse still didn't blow. At this point I didn't have the bulbs in the taillight or license plate sockets, so I reinserted those, and they lit up just fine.

Before messing with the connectors I was looking at the taillight wiring again while talking about the problem with my father, and I noticed the wires going from the reverse/turn bulb assembly to the running light socket had all been pinched, and one had the tiniest bit of copper showing, no more than 1 or 2 millimeters. It didn't occur to me at first that this could be a short, because those wires are only a few inches long and run around foam padding on the taillight housing. But then I realized the taillight housing presses the foam against the metal body of the car.

Everything seems to be working now, and I was extra careful to keep those wires free when I put the taillight housings back on, with a generous amount of electrical tape over the tiny nick in the coating.
We had replaced one of those bulbs a month ago or so, and must have got the wires caught in between the body and the housing when we reinstalled it.