Electrical draw issue

Some times life is just a :banghead: when it comes to old auto electrical issues. You could end up running around in circles if the problem is not completely corrected. I would bet all you need is a volt meter and time to find your problem/s: (even though your lights are acting up) Firstly as stated pull out all your rear lights one at a time and ensure the sockets are clean and they have good grounds.
My suggestion is that you first set your car up so all the conditions are "off" IE lights, radio, doors closed etc. At this state your vehicles battery should show no power loss or leaks to ground in a "corrected" condition. Anyways, put your volt meter to the DC volts reading....disconnect your negitive cable from the battery and meter between the neg cable and neg battery pole. If your meter shows any voltage or reading. this surely indicates something is grounded and slowly draining your battery.
Eight times out of ten a battery drain problem comes from your fuse box runs on the BATT side of things. (like a trunk light left on). Your Assisories or Start circut side of the fuse box runs could be OK.
Next, find your fuse box and have someone watch your meter as you lift one fuse at a time...(make sure your door is closed or the door button pushed in so conditions are correct and your using no power)..When, the correct fuse is pulled for that grounded run the meter should now show "no" voltage being used at the meter.... if this is the case, it will put you at a starting point. Some fuse boxes have the names of the componates on them IE lights, brakes, lighter etc. From there you will have to get some electrical drawings that show your electical runs. I hope some of this helps to get you on track. PS..I had a problem once where my trunk light adjustment button was out....It was hard to figure the problem out as the light was on with the lid closed lol.