The insulation resistance and interference rejection of several prototype thermal noise sensors were measured. It was found that twisting the connecting wires as a pair optimizes the magnetic interference rejection. High-temperature-resistant wire insulation was developed by vapor depositing a few micrometer thick ceramic coating. The best insulation was obtained with a coating of 1.25μm SiO2 + 1.5μm TiO2 + 0.25μm ZrO2. The insulation of four such coated pairs reached stable levels of 18 ± 3kΩ during a testing period of 1 week at 950°C under atmospheric conditions.