BMW DIY Replacing On-Board Computer (OBC) Illumination Lights E34 and E32
The OBC [on-board computer] light on my ‘91 525i just went out. I think you did a write-up on replacing the OBC light bar some time ago. If I remember, it was a pretty simple fix. My problem is I can’t find the article or the replacement light bar on your web site. Can you help me out?
The article you’re referring to was in the Spring 2004 issue of Fast Times. The reason you can’t find the light bar for your car is that it doesn’t use one. Instead, your OBC uses three individual bulbs to illuminate it. The E34 5-series (89-96 525i, 525it, 530i, 530it, 535i, 540i, M5) and E32 7-series (88-94 735i, 735il, 740i, 740il, 750il) use the same OBC design. You can access the illumination bulbs by removing the radio and then the OBC itself.
1) Remove the radio. Original BMW radio is removed by loosening the two securing screws under the small hinged flaps at the left and right sides of the radio, then pulling the radio out.
2) Once the radio is out, pull the release lever in the right rear corner of the radio cavity and pull the OBC out.
3) Once the OBC has been removed, you can simply replace the defective bulb(s).
The part number for the bulbs is 2721S (three required). Note that this part number is different from what BMW says is used. In this case the BMW “micro-film” parts look-up is incorrect. The BMW part number is a 6-volt bulb. The OBC needs 12-volt bulbs. The 6-volt bulbs burn out quickly.