Using the breakout box
WARNING: This page is about a different car, the 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.
Taking readings with the control module connected (circuit in operation)
The breakout box (the boxes) and adapter (981 3195) or (951 1351) are connected between the control module and the control module box connector. This allows voltage readings to be taken with the engine running.
Taking readings with the control module disconnected (split circuit)
The measuring box (the boxes) and adapter (981 3195) or (951 1351) are connected either to the control module connector or to the connector on the control module box. This allows resistance readings to be taken in each circuit without them being affected by other systems.