MyE28.com

'88 535is

This car had been sitting in my garage for over a year until today. While installing a new battery - old one was removed when the car was parked - the horn near the battery would go off everytime I connected the battery. I removed the horn for the time being and it is still out of the car until I can figure out why it was going off. The regular horn is still installed and operational at this point. My guess is it has to do with a factory alarm or something?

Anyone know what I should do to be able to install this horn back in the car without it continuously going off?

Thanks.

That is the OBC alarm horn and this indicates the OBC control is bad. You need to change the black box under the dash outside the steering wheel. A junkyard part should work fine. Probably a relay stuck in the box or something. Well tha tis my guess, anyway.

Either that or the horn relay itself is stuck. Swap that out for a quick way to eliminate one possibility.

The OBC horn relay is inside the OBC relay box. So it would be the box.