This is a copied post from the "So it begins..." thread. It is one of the repairs on my 1972 350sl euro. Hopefully this makes searching easier.
Well, here we go. It'll probably take longer to write this than it took to repair the sender (half hour max).
Here's the sender as removed
The hardest part to get past is that THIS actually is the nut that holds it all together. I had read of someone using needlenose pliers as a spanner, but I just loosened it with a pair of pliers
After disassembly, this is the rusted, varnished mess I had. Note the rust on the center post. This is why the gauge didn't read accurately and I'm sure why many complain about gauge levels suddenly dropping, or not moving at all.
You can see the float here, and if you look closely, you'll see 3 wires. 1 heavier gauge copper (ground), and two REALLY thin wires for the resistance circuit.
The end cap is made up of a washer and plastic "maze" end cap. The "maze" acts as a dampener so the float doesn't move as quickly as the fuel level sloshing in the tank.
This shot is AFTER I've cleaned it. It was crusted with varnish and corroded. Here's where I pass on a little secret.. ever tried that glass and bathroom cleaner Kaboom? Well, it's a relatively strong acid, but acts just slowly enough to gauge the cleaning. This is the original sender from '72 and it is literally good as new. It also work GREAT on window glass.
At the bottom (where the nut goes) are the terminals for the wires. The 2 pins you see are if you have a low level sensor.
This closeup show the contacts on the float as well as the ring that touches the 2 terminals for the low level sensor
This closeup shows the "maze" end cap and how (after cleaning) it's path allows fuel in at a slow enough rate to dampen sloshing fuel
This was not hard at all, you just need to be VERY careful not to mess with the wires.