Delica Canada | Mitsubishi Van Club

Both plugs stopped working, I blame myself for having tried a 12V tire pump in them. The rear accessory plug has a 20A fuse but maybe, being 21 years old (May 1994 model), the old components just couldn't take the load.

The fuses are all fine, so I thought it might have been the plug itself (I hear it has a metal fuse of its own), but after replacing the rear accessory plug, it still doesn't work.

I must say the wire for that thing is the thinnest wire I've ever seen, it's like the ones we used to use in electronics class in the 1980s for HeathKit logic circuit kits. I am wondering whether the wire itself burnt somewhere between the batteries and the rear.

Meanwhile the lights for the inclinometer and V meter in the center console are flickering, I suspect a loose connection somewhere but hopefully it's not a short (?).

You're dead right about the wire used on the Delica looms, at least on my L400. I wouldn't put any more than 5A through many of the circuits given how abysmally small a wire gauge was used. It sounds unlikely that you have a short circuit, at least not downstream of your fuse.

Given that you appear to have hands-on experience with circuitry, there are a couple of things you can check with due caution:
- take out the respective fuse(s) and with a multimeter on DC volts check for 12V against ground on both fuseholder terminals with your ignition switch on acc. You should have 12V on the input side. If not, look for a break or other interruption in the conductor on the upstream side, closer to the source which is your battery.
- while you're at it, check the output (currently dead) fuse terminal for continuity to ground using the ohms range on your meter. It shouldn't give you a reading, at least on low ohms range.
- check that you have good continuity from the outer shell of the 12V plug to ground.
- with the fuse still out and preferably with the battery disconnected, short the fuseholder OUTPUT terminal to ground with a length of wire then go back to your plugs and check for continuity from the centre contact of each to ground. If nothing then you likely have an open conductor in the cable loom. Not good.

20 amps is a big current for a small gauge wire to handle and it's likely it could have gone open circuit before the fuse could blow to protect it. Hopefully not ! If that is the case and you can't find the break then your only recourse is to run a new cable (something decently solid like 12 AWG) from the battery via an inline 20A fuse to the plugs.
I have installed a dedicated 12V accessory plug for heavier loads this way to avoid exactly the problem you have there.