electrical gremlins in the 87 300d - PeachParts Mercedes-Benz Forum

Jim Wickham · #1 07-02-2007, 09:54 AM

1. The PO had an aftermarket SONY cd player in the car it seems to operate fine until you shut the last door on the car. What would cause this?

2. Hazards don't work and when the headlights are on the hazard button on the dash is red. I hear a click randomly that sounds like a turnsignal over by the glove box. Could it be a bad flasher unit?

3. Headrests in the back are up and I think there is a button on the dash to get them to go down but it doesn't seem to do the trick.

any info is greatly appreciated.

Jeremy5848 · #2 07-02-2007, 12:18 PM

Quote:

Originally Posted by Jim Wickham

3. Headrests in the back are up and I think there is a button on the dash to get them to go down but it doesn't seem to do the trick.

My wife's 87 did this also so I ended up pushing the rear head rests down by hand after pressing the switch. The mechanism works by vacuum so I'll probably check all of the vacuum lines, etc., looking for leaks. My wife doesn't use them so it hasn't been an issue.

Jim Wickham · #3 07-02-2007, 12:23 PM

How much pressure did it take to get them to go down?

babymog · #4 07-02-2007, 01:46 PM

Sony problem sounds like it's running on the courtesy light power.

The hazard light switch is supposed to glow when the lights are on.

Headrest is controlled by vacuum, sometimes it takes holding the button down for a few seconds, and the engine has to be running to create vacuum I believe, ... I don't think it runs from the vacuum pump under the rear seat. The switch operates a NC solenoid under the left side of the rear seat cushion. If you can't get it to work, check for voltage there with the button depressed. You can also manually drop the headrests from that point by simply sucking on the vacuum line that goes up under the rear seatback for a few seconds, they'll drop eventually.

Jim Wickham · #5 07-02-2007, 02:36 PM

Quote:

Originally Posted by babymog

Sony problem sounds like it's running on the courtesy light power.

The hazard light switch is supposed to glow when the lights are on.

Thanks babymog, follow up questions.

What power should I try to tap into under there for the radio, or should I just get my volt meter out and see what has power under normal ignition on status?

Would the hazards not work because of a bad flasher? like I said I hear the random clicking when I'm driving down the road and it really does sound like the flasher. Is it located near the glove box?

babymog · #6 07-02-2007, 06:55 PM

Wish I knew on the flasher location, and whether it shares the turn-signal one, ... but I don't. If you're in a pinch I can look in my parts car (with dash currently removed) for flasher, but someone here will probably beat me to it.

In the radio area, you have IGN+, Constant12V+, Antenna, Speakers, and IP Light+. Should have what you need, test with a 12v light, not a meter is preferrable.

Car stereo installers, ... don't get me started.

pmckechnie · #7 07-02-2007, 07:06 PM

On the radio, I would recommend you check the ground wire for the radio. See if it was hooked to the wire for the interior lights. With the doors open, it will show a ground but show +12 when they are closed. Thats the only thing I can think of that will give these symptoms.

Jim Wickham · #8 07-02-2007, 11:01 PM

looks like the voltmeter and I will be spending tomorrow evening together.

Thanks again guys for the help

Jeremy5848 · #9 07-02-2007, 11:35 PM

(That crack is aimed at me, not you!)

So I read the owner's manual....indeed, the engine vacuum is used to lower the headrests so the engine must be running, then press the switch and they should go down. I didn't have to press very hard to get them to go down, as I recall. Then again, at that time I didn't have the manual and probably tried it with the engine off.

Getting the headrests up, simply lift by hand. This allows the rear seat passengers to participate in the operation of the vehicle, especially good for those with emotional problems.

Jim Wickham · #10 07-03-2007, 08:30 AM

Hey I have a manual too but it is more fun and interactive to get information here. especially when the manual is really vague about something.

Jim Wickham · #11 07-04-2007, 07:15 PM

I have an update.

Got the radio working with the doors closed. Until I turn on the Hazzards, then it powers off and the hazzards don't work at all until I open the door back up.

I have two switches on the door jam. The top one does turns on the courtesy/entrance lights. I can not figure out what the second switch right under it affects other than if I push it the hazzards shut off.

Can anybody tell me why that might be?

Jeremy5848 · #12 07-04-2007, 08:25 PM

Quote:

Originally Posted by Jim Wickham

I have two switches on the door jam. The top one does turns on the courtesy/entrance lights. I can not figure out what the second switch right under it affects other than if I push it the hazzards shut off.

Can anybody tell me why that might be?

The second door jamb switch is connected to the "warning relay," an electronic device (not just a simple relay) that lives behind the instrument cluster. It operates the front dome light, the seat belt buzzer, and probably other things -- I forget. In my case, the relay was defective; replacing it got a lot of things working, although I had other problems too.

Jim Wickham · #13 07-04-2007, 09:24 PM

found it... combination of some cobbled wiring and a dead fuse... replaced the fuse and now I have radio everytime the door is closed, and I have hazzards anytime I put them on.

babymog · #14 07-06-2007, 11:19 PM

The second switch is for the security system (brain under the passenger's feet).

darkman · #15 07-07-2007, 01:49 AM

Hi all,
I'm wondering if this is the answer to a gremlin of mine that I had forgotten about.

What's the relationship between the courtesy light and radio??

When I first got mine, the courtesy light would not go out on the right rear door.
Of course, it killed the battery.

I just unscrewed the bulb and eventually forgot about it until reading this thread.

Later, when I installed an aftermarket CD head unit, I saw that the PO had removed one and
re-installed the Becker before passing the car to me.

I never imagined a connection between the stereo and the courtesy lights
until now. How does it all hook up? Is there something I can look for?

Thanks guys