Discoloration on contact surfaces is a sure sign of contact failure.

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Visual signs on contact surfaces aren’t definitive proof of failure. Discoloration can arise from heat exposure, oxidation, humidity, or protective coatings and may occur without any functional failure. Conversely, a contact can fail due to wear, pitting, misalignment, or insulation issues that aren’t visible as discoloration. So, you can’t conclude that discoloration equals failure just from appearance. Reliable diagnosis comes from combining visual inspection with measurements and tests, such as checking contact resistance, monitoring temperature rise, looking for arcing or pitting, and confirming proper fit and alignment.