Fretting tests of tin-coated connectors are often performed at exaggerated vibration levels, followed by measurement of the contact resistance. However, the strong vibration might cause stochastic penetration of the vibration induced oxide layer, and the connector might pass the test despite almost the entire contact area being covered by an insulating oxide layer. Therefore, in-situ detection of micro-slip at the contact interface during vibration would be desirable, since micro-motion is a prerequisite for fretting. In a previous study using model contacts, it has been demonstrated that oscillating slip will result in a detectable noise of the contact voltage drop. The electrical noise is probably caused by changes in the pattern of a-spots during the oscillating micro-slip. In this study, it is demonstrated that it is possible to measure the micro-slip induced electrical noise in real connectors. Thus, the vibration threshold level when the micro-slip starts can be determined in situ. Furthermore, this can be performed without influencing the dynamic behavior of the connector or changing the contact interface.