Electrical fault in a ’99 2.5 20V V70.

The first sign of the problem was a flat battery after few days of
non-use. Further investigation indicates that the engine system
circuit is not shutting down when the ignition is turned off. This is
evident in that the relay is not powering down and resetting and as a
result the engine management components continue to draw power.
However, if the Engine System Relay (in the Main Fuse Box) is
disconnected and reconnected, or the battery is momentarily
disconnected, the circuit shuts down and remains shut down until the
ignition switch is powered on. The problem will then reoccur when the
ignition switch is turned off.
The relay itself is OK, the issue is that the relay is still powered
when the ignition switch is switched off. Whatever is activating that
relay is not reset until the battery is momentarily disconnected or
the relay itself is disconnected and reconnected.