Which parts of Andalucia - it's a very big province, but then the whole of Spain is a network of tracks. Fire breakers are illegal to ride and if there's a chain across a track, it's usually there for a reason.
Military maps are the most accurate and show tracks. You should also have a look at this site Visor SigPac
which uses a combination of military maps and satellite imagery.
Be careful going off-road if it rains. The red earth turns to clay which is impossible to clean off and can be very damaging to bikes. A friend of mine was out trail riding last week and went through what he thought was dried mud. He ended up in a foot of wet mud and it took 6 grown men to pull the bike out. It doesn't rain often, but when it rains, it rains a lot and the recent flash floods Spain has been experiencing have been deadly, so take care!
I can recommend a good campsite close to us - we're holding a bike meeting there this weekend. People have arrived today a day early and they have said the site is very good, excellent facilities and good food in the restaurant. There is more info about the campsite on the link below.