مقاومة عالية في أسلاك الحساس

A connection that still conducts but no longer conducts freely — a corroded terminal, a spread contact, a strand-broken wire under intact insulation. This is the most deceptive wiring fault there is, because continuity tests pass. A meter reading a complete circuit says nothing about how much voltage that circuit drops once real current flows through it.

On a signal wire the effect is a reading that is consistently wrong rather than absent, which is why it so often presents as a drifted or correlating-badly sensor and gets a new sensor fitted for nothing. On a heater or supply circuit it is worse, because the resistance turns into heat at the bad joint, which oxidises it further and accelerates its own decline until the terminal burns.

Voltage-drop testing under load is what finds it, not a continuity check. And a connector showing discoloured or melted plastic around one terminal has already declared itself — that browning is the visible history of a connection that has been failing for a long time.