Help Firing Dad's Dart up Again - SOS - No Spark After Hosing Off the Dust

For a little backstory here's a post I made a couple of years ago about my Dad's '74 Dart Sport.
Starting a Slant for the first time since 1986 - Slant Six Forum

Long story, but he's finally just said "this car is up to you boys", so "us boys" are doing a pretty massive overhaul in the next 3-4 days while Dad is visiting me for Christmas to get him a big jump start on getting him back behind the wheel before he gets any older.

We've got a part that they need help identifying. It appears to a relay of some sort mounted behind the battery tray on the driver's side fender. Anyone know what this is?

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