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1990 300TE
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129 Posts
Discussion Starter · #1 ·
I'm blowing 25 amp fuses every time I try to move the driver's seat. I don't try multiple directions at once, just trying to raise the back of the seat from a semi-recllining to a driveable upright position. Where should I start looking for the open circuit? Anybody have any experience (e.g. luck) with this type of thing?

Unintentionally "low riding" in Alabama -

Paul
 

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E320 wagon
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953 Posts
Most likely the door control switch , easy to change . see if the fuse works with left or right door control disconnected . Does the seat move before the fuse blows ? .
I have seen mechs put a rod in the fuse holder , move the seat quickly to a good position and remove the rod , this risks burning the seat wiring if the motor is shorted .
 

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About a dozen 1988, 1989, 1990, and 1991 sedans, wagons, 4Matics and 1 coupe
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I'll tell you this, the power seat wiring in these cars is pretty funky. I'm intimately familiar with it because i recently installed the whole power/memory seat/column setup from a 300E in my 260E. There's a LOT of wiring involved.

For one thing, did you know that unlocking and opening either front door allows you to operate the power seats without ever putting the key inthe ignition? One of the two door jamb switches on either side is used exclusively to energize the power seat relay in the main fuse box. This is a nice feature becasue it allows you to use the memory seat buttons to adjust the seat to your desired position before you get in the car.

As far as your particular problem, MBZ is kind enough to used several different connectors to the memory seat module and you can hotwire the backrest adjuster motor from there. That way you can bypass the door switch and the miles of wiring between the door switch and the underside of the seat. I'll take a look at my wiring diagrams tomorrow morning and post details.
 

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1990 300TE
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129 Posts
Discussion Starter · #4 ·
Thanks! I'm no electrical wizard. I just want to know where to start. One piece of unsolicited "advice" from someone was to:

'Stick a penny in the fuse holder, try to move the seat, & then see where the smoke comes from - you've just located your'e problem. Just replace whateverer burned up and go from there.'

I'm not quite to that point, but I am aware of the open door ability to move the seats - My Benz also has the memory button & there's about $200 worth of copper in the seat wiring.

My favorite remark on the "snarl" of wiring comes from Star Trek's 'Scotty' - "The more you complicate the plumbing, the easier it is to stop up the pipe."

Paul
 

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E320 wagon
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My seat are on two different fuses , fore & aft base / roll of total seat back & seat on 1 . Number 2 has back rest only / head rest. I have lost 2 and replaced the switch.
 

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1990 300TE
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129 Posts
Discussion Starter · #6 ·
I have the same setup. Also, the driver's side has the "green" memory button. I didn't quite understand. Did you say you had both seat adjusters (driver & passenger) switches go bad? If so, then I know where to start looking.

Thanks,

Paul
 

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About a dozen 1988, 1989, 1990, and 1991 sedans, wagons, 4Matics and 1 coupe
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Okay I've taken a look at the wiring diagram for the driver's side memory seat setup. Call me skeptical but I'm having a hard time blaming the door control switch for blown fuses. That's because wiring (2 circuits) goes DIRECTLY from the fuses (E & F) to the seat memory/control unit. That unit is kind of built into the base of the seat and it has a bunch of connectors going to it -- like 8 of them... The door switch simply provides control signals to the module and it then operates the seat motors.

To cut to the chase, you want to unhook the carpeted panel (that hides the seat mechanism) at the bottom edge and lift it up as best you can. Not a lot of room there, I know. Then look for the connector that contains the red, orange, green, brown, and yellow/red wires; thats the one containing the recliner motor/position sensor circuits. Unplug the connector and use jumper wires to plug into the green and orange wires -- they're the ones that operate the recliner motor. I use my cordless drill battery pack to move seats in junkyards and it works like a charm. Anyway, use your battery of choice to move the recliner as necessary.

At this point I'm suspecting that the seat memory/control module is bad. Does moving the seat fore/aft or any other way blow the fuse?
 

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I had a door control that shorted , it would run fore & aft , but short out in the middle. I am guessing its a three wire motor with a common center tap winding , with the springs gone in the switch contacts , it would short to both outer leads. I would try it by removing one door controller .
 

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1990 300TE
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Discussion Starter · #9 ·
Augapfel -

The unit blew fuses on any setting. If I tried to move the head rest, seat, back, anything. I say "blew" because I took the cover off the driver's seat control on the door, and then put the cover back on. Whatever was causing it isn't active anymore; I'm sure that pulling & putting a cover on had nothing to do with it.

I stuck a phillips screw driver head in the fuse holder to quickly raise the back of the seat so I could at least drive the car. The head wasn't even warm. I put the 25amp fuse in and have had no more troubles.

go figure.

Thanks for all the help! I'm sure I will need to reference you and all the others' emails in the future - at least as long as I drive a MB (e.g. lifetime).

Paul
 
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