focus dashboard lights.going off?

hi,i have a 98,s reg focus zetec 1.6.recently my dashbord lights have started to go off,making my speedo etc unreadable in the dark,before this happened,my speedo,didnt always start working straightaway,it kicked in after a few mins.also,the rear offside passenger door central locking doesnt work,could this be related?.one more thing,my car has no oil leaks,but is using a lot of oil,im putting a litre a week in,could this be the age of the car,im a learner driver,got this car for £400,everything else is great,