Sorry got a later engine, but wherever it is it'll have 2 wires to the distributor and one each to the coil, battery and earth - so five wires in all.
Ignition ampliifer (ecu it's not) is located between battery and headlight on mine, so that could be a good place to start looking. Corroded, frayed or disingrating wires are a more likely culprit than the box itself.
This page might help identify connectors:
https://www.prancingmoose.com/volvoh...html#240series