I have 2002 Ford Focus, My dashboard lights and headlights are surging and I don't know what could be causing this.

My husband has a ford 500 that did the same thing and it was an electrical problem. Go to the dealer and get it checked out

Do you have a powerful amp and speakers installed? If so, you may need to install a 1.5 to 2 farad capacitor. If not, check the battery, alternator, and main ground (corrosion). My bet is that the alternator is bad. This link may help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-10.html#post1973613

Look for 14 to 15 volts at the battery, while the engine is idling.