My reverse lights were working, but aren't now. The car sat for a long long time and is now running and driving. What are possible causes and solutions please? Obviously I've checked the bulbs - that's not it.

Thanks for the help! It's got the pushbutton auto, fyi.

I would start by checking your connections(grounds, contacts etc..) most likely a contact has some corrosion or dirt causing it not to work. Since it sat for so long the new attention has stirred the gremlins, you'll find the culprit soon enough. Another thing I've had good luck with is when I'm messing with the connectors & such I liberally spray lubricate on the pieces. Little messy but seems to work great!!