1990 SEC Heated seat woes - Mercedes-Benz Forum
 
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post #1 of 8 (permalink) Old 06-11-2019, 12:32 PM Thread Starter
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1990 SEC Heated seat woes

Hi All,

I've had my 1990 500 SEC for a few years now and it's mostly been smooth sailing. Today, however, as I was driving home I noticed all the heated seat LEDs were on but the seats weren't heating up. I hadn't switched them on. They'd worked faultlessly up until today, and now the LEDs are staying on even without the key in the ignition. They don't turn on or off, just all four LEDs (driver and passenger side) are on constantly, but much fainter than usual.

I pulled the fuse, but still they're on. If I press the switch, they fade out to nothing but as soon as I let go they start glowing again. Appreciate issues with heated seats are commonplace but I am struggling to find much info.

Any advice much appreciated.

Thanks!
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post #2 of 8 (permalink) Old 06-11-2019, 01:07 PM
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This pic shows a control unit for the heated seats which may have died. Good luck and let us know what you find.
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post #3 of 8 (permalink) Old 06-11-2019, 02:57 PM
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Yes i would suspect the relay, which would be a nice easy fix.

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post #4 of 8 (permalink) Old 06-12-2019, 01:36 AM Thread Starter
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Thanks for the responses.

So, the plot thickens as of last night. I investigated the unit under the drivers seat, then went round to the passenger side to look under the seat there and found about an inch of water in the footwell. I reckon that must be why we had some very heavy rain and the car was outside (usually garaged). The electrics under the seat are just sitting in water. I suppose now my job is to find out where the water's getting in...
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post #5 of 8 (permalink) Old 06-12-2019, 02:07 AM
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Ah that makes sense then. There are a lot of potential entry points for water, cars in general are a pain in the arse when they leak. First port of call should be checking that drains are all clear. If you search the site there should be a PDF somewhere of all the drains. Sunroof has drains on each corner of the unit. If you can take off the scuttle cover after removing the wiper arms, there are two big drains there too. Check for rust also.

Come back to us with what you find. If these are OK we can tell you what else to check.
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post #6 of 8 (permalink) Old 06-12-2019, 09:47 AM
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An inch! I wonder if the electronics can be dried and saved?

When my wife's coffee maker displayed an error message, of course I took it apart and found the bottom of the board soaking wet and a transistor with one of its "legs" rusted apart. I replaced the transistor and resealed the board enclosure and it works again. Of course, she'd already bought a new one. Oh well, my daughter said she'd take it.

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post #7 of 8 (permalink) Old 06-12-2019, 09:48 AM
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Yeah these components are tough as old boots.

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post #8 of 8 (permalink) Old 06-12-2019, 12:54 PM
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probably totally different entry point..but on my old 2002 BMW 540..those were notorious for leaking vapor barriers behind the rear door panels. Water would come down behind the rubber seal outside the door/by the glass, and instead of draining through a designated drain hole at the bottom of the door, the water would come onto the doorsill, up and over onto the carpet. Especially when the car was on a hill/parked on a slant
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