cig lighter not working when car lights are on
 

Got a classic impreza, problem i have is that the previous owner bodged some of the wires behind the cd player and basically the cig lighter wasnt wired in as the wires were cut.
It wasnt clear from the wires that were there (not attached for stereo use) which wires i had to reconnect to.
So i found a pair of free wires to wire to the cig lighter that were positive/negative.
Problem is that now the cig lighter only works when the cars sidelights/headlights are off.
Any idea why the cig lighter doesnt work when the car lights are on?
Before you ask i'm not using it for lighting cigs its for sat nav :)