Clock problems.

I am having problems with the clock light on my 87 325. During the day i can see the clock display but at night when i turn the head lights on the clock display goes off.

The clock/computer displays are backlit by LEDs. Remove the panel and replace the burnt out LEDs.

I've had two older 5-Series with computers and had to replace the backlight in both of them--so the principle ought to be the same with your '87 3. There is likely one bulb in your computer--it's not an LED, but a very small (less than fingernail size) bulb that probably goes in from the side. The computer in my 535i actually comes out of the dash (next to the radio) pretty easily. In my 528e it was next to the instrument cluster (which you had to remove), and then a white "bulb tray" costing $27 pulled out sideways relative to the computer. Your 3 Series is probably more similar to my 535i in that you have to remove the radio first and then you can slide the computer out of the center dash (I'm assuming you have the computer--don't know about the regular clock although it may be similar). If there are more than one bulb, I'd suggest replacing all of them at the same time. Bulbs for my 535i computer were $1.05 each from the dealer.

I'm a bit confused why it would light up during the day but go completely dark at night--usually the display will just go dark all together.

Anyways, hope this helps, and let me know if I can explain (confuse?) things further.