I was dealing with corrosion in the 40 year old harness at the fuel sender connector (lack thereof).

When I removed insulation to expose copper, it was clear that moisture had entered the harness and seeped in.

Rather than replace a large piece, I simply used steel wool to remove the corroded outer layer to expose copper that was suitable for soldering. Fortunatley the copper was not brittle and had a reasonably flexible core.

Wires on left are the 240z harness leads to the fuel sender. The wires on the right and scavanged wires with connectors that I wish to connect to the harness. Note the different colours of the exposed copper.

Here are the same wires after a little TLC from steel wool:

Use flux, plenty of heat and a heat sink to protect the insulation. That will give you a long lasting solder joint.