1994 Volvo 850, no spark, ECU??

[Ozark Lee]

It is not uncommon for either the flywire that plugs into the socket to break (usually right where it goes into the box) or the contacts under the button to get corroded and not make good electrical contact. Both are easily fixable.

The button box itself has a connector on the bottom where you can unplug the box from the wiring harness. If you unplug it you can remove and disassemble the box, clean the contacts, and repair the flywire if necessary. There are four locking tabs that hold it together but take it apart slowly so that the spring under the button doesn't sail and get lost. If the flywire is broken you can cut the wire at the break, strip back the insulation, and solder it back onto the contact.

...Lee