Electrical Gremlin

Started the Land Rover a few days ago, and promptly lost the brake lights, turn signals and heater. Everything else was fine, vehicle ran smoothly, no smell of burning, etc.. Electrical issues are not my forté, and so was worried that this would be difficult to solve. Luckily, I like to keep the Land Rover clean to ward off corrosion, and so a visual inspection of the wiring wasn't too difficult to do. Nothing appeared amiss. Jiggled all the connections. Fuses were intact. What was the source of the problem?

Knowing that many of the Lucas issues were due to corrosion (perhaps due to connectors being aluminum bullets in steel sheaths....), connectors along those paths were examined, but all looked like the day they were installed. Then I took out the fuse again, in case there was some invisible cold- or condensation-related problem (it's been anywhere from 0°C to -20°C recently), and put in the spare - and voila, the Land Rover was back to normal. I put the original back to see, and things were still good. Source of the problem? A very thin and practically invisible layer of dirt or corrosion on the fuse-holding tongues/clips. Gave them a thorough clean, and everything works again.

Tongues in question (orange arrows):