an automotive electrical system including a wiring harness incorporates a dedicated test line passing through critical connectors and components for allowing detection and isolation of improperly connected connectors . the dedicated test line can feed through expansion connectors , termination connectors , and junction blocks . connector fault detection and isolation can be performed as a test after final assembly and during vehicle servicing . a large number of expensive and inconvenient vehicle quits and tow - in &# 39 ; s are avoided that would otherwise occur .