Situation:
I'm trying to see if my new sub box securing system is any good, so go for a quick bit of lane driving. All is well, until 10 mins in, sound stops. Grand... blown it 15 mins after being in the car. Hand on amp... yup, toasty, must have hit the thermal (swear at Sony for inefficient design). Get home, sub box still in place, good stuff

Look at all the fuses, all is good, multimeter the power and remote cables, all is good. Must be the amp...
Look at amp, all good, check all terminals, ok, right forget it, and leave indoors for a few days, good excuse to fit my V12 to Fake instead. Slight incling it could be a not perfect earth. As I had the panels off yesterday to fit some more gauges, put a multimeter there, and nope, resistance check is all good, so stick some bits of wire on the amp power terminals, and hang on... when you hook it to the battery, it works... hmmm, ok, wire it all up... it doesn't.
Here is the culprit:

Dodgy contact between fuse wire and end cap. Looks fine, but there is a silly high resistance there, so 12V can be seen on the meter, but no useful current can pass. Weird thing is it's the same fuse I bought and used in Kar (as all my spare big fuses are in Soton, and I'm not) but had to go and buy some more today

That long story, which didn't need to be that long at all, is to highlight the don't trust nothing... test and test again school of thought!