For the lights, check the quality of the bulbs you are using. E32s/E34s have finnicky LKMs (Light Control Module). Cheap bulbs give too much resistance and throw a code. (Can also be caused by cheap aftermarket tail-lights or bad bulb holders.)
The solution is to either buy the bulbs at the dealer OR get Sylvania EURO bulbs at pep boys. The euros have plain aluminum-looking bases where as the "regular" ones are brass colored.
As for the computer bulb, if you take out your radio, there is a lever on the side of the computer to get it out. Replacing the bulb inside the unit is fairly self explanatory. DON'T FORGET TO GET YOUR RADIO CODE BEFORE DOING THIS!!!
Full DIY with pictures. Should be the same for the E32.
BMW E34 Website