What Is Excessive Resistance In A Car's Electrical System And What Is Its Cause?

Excessive resistance is usually the cause of higher than normal voltage drop. What happens is that a load or loads in the circuit attempts to draw its required current. But if there is excessive resistance in either a wire or a load, it can have the same effect as the circuit being broken - no current -  if the rise in resistance is sufficiently high.

Excessive resistance can catch out car maintenance enthusiasts as the symptoms are the same as an open. Most times though excessive resistance will be signalled before  the current fails completely. Tell tale signs of excessive resistance are components in the circuit operating at reduced capacity. Typically, this will be such things as headlights etc. appearing dimmer than normal or electric motors running at speeds slower than normal.

Fortunately, excessive resistance is often easily cured as the cause is normally nothing more sinister than dirty or corroded terminals or contacts. Sometimes, however, the cause is a partially chafed or broken wire not having a large enough cross section through which to allow current to pass.