The Seat had two. The first turned out to be a burnt out fuse, so once that was replaced, the windscreen wipers worked again and the second was a rear hatchback lock that was frozen. Parking it so that the rear door was in the sunshine for a morning cured that.
The small Nissan had a non-functioning heated read window. After the fuse was checked and found to be OK, the connectors were taken off, and the terminals rubbed with an abrasive cloth to remove the layer of oxide that had built up. Upon re-assembly the heated rear screen worked fine.
Both the boys were highly appreciative of my efforts and it is satisfying to be able to pass on simple tips that will avoid the cost of involving a profession mechanic. One just hopes that the my beloved sons will remember the steps we have taken together to resolve these problems when they come to tackle any further hiccups and try the simple things first. However, I fear I have not heard the last conversation that starts "Dad, I have a small problem with my car......."
Lots of Love, Guys.