1986 420 SEL Freaks Out!! What Just Happened??
 

Washed the 420 this afternoon then took it out for about 5 miles. As I was turning into the drive the headlights, already on, started flashing and some sort of horn-like device started sounding repeatedly. This lasted maybe 5 seconds, then it stopped. I drove up to the garage door and stopped; engine was running normally, etc.
Was this some sort of alarm system? I've owned Her 6 years and never had this happen before.

Answer
 

Factory Alarm System Issues
http://www.peachparts.com/shopforum/diesel-discussion/150748-factory-alarm-system-issues.html#post1143583





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Check door handle plugins inside door, most likely water got into plug , dry or seal the male /female plug so water cant get in (if water is found in plug/connector) only front doors have plug water issues

My W126 did this about 20 months ago... it did it random for a week, then quit on its own and hasnt sounded off randomly again.

W126 Factory alarms suck. You'll want to remove it. It's under the passenger side kick panel. It's a black box with two large wiring harnesses attached, and if the sticker is still on it, it says "Becker Autoradio"

You can just unplug both harnesses and everything will be fine.

'86 420 SEL Freaks Out!! What Just Happened??
 

Just now ripped mine out with impunity on the side of the interstate. If anyone needs the factory alarm, theres one in the median of I16 at mile marker 157.

Heres what it looked like after a bare handed uninstall.

http://img.tapatalk.com/d/14/03/06/asydepa3.jpg