My Guys Are Stumped - 1987 Mercedes-Benz 420SEL

This question has all our technicians stumped.........
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The vehicle currently has the following problems:
1. The front overhead light would stay on even when the key is out and all
the doors are closed; it could be turned off only with the overhead control switch. 2. The master key would not engage the central locking/unlocking system. 3. The door lights, rear overhead and reading lights, as well as the trunk light, would not go on. 4. When the engine is running, the overhead seat belt warning light keeps blinking.
These are all resulted from replacement of the #15 fuse (8A). Last week the power antenna started not extending its mast, and the front overhead light would blink every time I turned on the radio.
This afternoon, I check the fuse box and noticed the #15 fuse was burned out. So I replaced the 8A fuse and operated the radio a few times to observe the power antenna to extend and retrieve its mast.
After a few times the power antenna start the same problem and the #15 fuse would go out again. So I unplugged the power antenna unit connector and replaced the #15 fuse.
But the #15 fuse would burn out the moment it was in the slot. I then noticed that the front overhead light would not go off on its own when all the doors are closed, unless I turn the switch off.
I then disconnected the (-) battery terminal for more than 20 minutes.
When I connected the battery terminal back again, with the #15 fuse out and the power antenna connector disconnected, the vehicle seems to run just fine, except the 4 noticeable problems described at the beginning.
Please advise."
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If you want to answer online, that 's great. The question is at: http://www.all-parts.com/diagnostics/kb2.php4?view_open_thread&id 820
He's offering $7.50.
THanks
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Suggest you temporarily remove the seat belt warning device - the little box/buzzer that controls the driver's seat belt vs. the seat belt buzzer, the overhead light when the driver's door (only) is opened, and the buzzer when the headlights are left on after engine shut down. It may be part of the car's problem.
The other items - power antenna, blown fuses etc. suggest a pinched wiring harness - any wrecks?
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BTDT. I had simlilar woes. Turns out it was an aftermarkey phone wire for an old hansfree.
So, first thing I'd to is to disconect any third party add on stuff like steros or phones.
Next thing I'd check is to see if all your grounds really are grounds.
If its still nox fixed then stare at the schematics long enough till you find something in common with all the failed circuits. Then start there and find where the electrons stio or where they are where they shouldn't be.
The fact the radio flickers means it's getting intermittane power - you've got a loose something someplace.
--
Need Mercedes parts? http://parts.mbz.org
Richard Sexton | Mercedes stuff: http://mbz.org
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for the overhead light, consider the door switch/plunger. it may have worn and giving indications that the door is open, ergo the overhead light stays on. causal effect may also include the seat belt chime ? i dunno, just keyboard thinking.....
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