Plug connectors and relays are a somehow “neglected” root cause in failures of microelectronic and power electronic systems. If application and dimensioning has not been done correctly, it may end in severe functional and/or fire disasters. This tutorial accompanying paper reviews the most frequent failure signatures and root causes considering plug connectors and relays. However, these components must not be regarded separately from their interactions with their neighbourhood when discussing failure mechanisms. PCB-bending and bending-sensitive neighboured components, voltage- and/or current-overload, corrosion, material selection, fretting and sportive specifications should get more in the focus of forensic failure analysis experts for root cause finding.