GP-light flashing, brake-lights working fine - code indicating brake switch failure

[sjurea]

Caddy 2002 7kvf @ 155000 km. I had just fixed one problem, and an hour or so later, it hit me with another. The GP-light started pulsating. I videoed it on the spot:
https://www.youtube.com/watch?v=qtoAi7jAI2Q
I read up on here, and checked the brake light switch for corrosion. There was none, and the piston moved like it seemingly should. I reconnected it and tested the brake-lights. They work fine. See video:
https://www.youtube.com/watch?v=okeTqkS6vlQ

I pulled the codes: 17655 - Needle lift sensor (G80): Open or short to plus. P1248-35-10 - intermittent. This code would not go away when deleted, but the brake lights still worked normally.

I then removed the switch, and tested its four connectors for continuity. The only pins with continuity were the two middle ones, with less than 1 Ohm resistance between them. Here are pictures of the switch and its connector: (No identifying number on it.)

 

[sjurea]

Edit: I opened up the brake switch, and looked for corrosion. There was none, bar a thin, grayish film, resembling galvanization, or possibly the oxidized surface of aluminium. I sanded it all down, took the switch mechanism apart, and reassembled it. That was a complex task, which required some thinking. It's five parts that all move in relation to one another, and it won't come together, unless the pieces are positioned right relative to each other, at each sequential step.

I put the brake switch back in, and gave it a go. The brake lights still work normally, and the GP-light is still pulsating. I deleted the code, but it kept coming right back.

I then found another grounding-point.

I cleaned that, but to no effect. I had cleared the point under the battery before too. Anyone know of other grounding-points on the ALH?

 

[sjurea]

I checked resistance through the glow plugs - slightly less than, or at, 1 Ohm for all of them. The contacts all looked shiny.

It is winter her in Norway now. The car starts, but starts rough. It's skipping a quarter, or so, of the beats for the first half minute, or so, after startup, and there is lots of heavy, acrid, white smoke. It runs just fine after that, though.