86 300e seat adjustment

Suddenly I cannot adjust either of the front seats. it isn't the fuse. what else could it be? thx

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snipped-for-privacy@alveus.com (kbm) wrote in message

HELP PLEASE
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Some places to start looking:
There is a fuse feeding the relay (16A?) in the fuse box. There should also be power fuses (25A?) from the relay to the seat switches.
If all good, check if the relay is working.
Also possible is a problem in the door switch circuit that controls the relay (your seats move with ignition off and doors open).
The seat switches themselves are known to go out on these cars too - but usually not all 3 sections at once. A bit expensive, but easy to replace.
Scott D

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snipped-for-privacy@alveus.com (kbm) wrote in message

Thanks Scott. I checked the fuses. The fuses for each front seat look good. I replaced them anyway but still doesn't work. I figured that since both front doors went out at exactly the same time it probably was't the fuses.
Where is the relay and how do I check it?
It seems like if it was the door switch then it would not function with either the ignition on or doors open but if you can't adjust the seats with doors open nor with the ignition on it doesn't seem likely to me. But I am not knowledgeable in these things so anything you can suggest would be helpful and appreciated.
I noticed last night that the dome light doesn't come on when I open the door and none of the 3 settings work when I switch it on from the inside. Is this related?
Is there a way to manually adjust the seats? The passenger seat with the back all the way reclined.
Thank you for all you help.
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From the fact that they do not work with either the doors open or with ACC power on, it could be the relay but you should check everything else too. There are 4 fuses to check. The relays are in the rear section of the fuse box but I cannot remember which one is the seat relay - maybe your owner's manual will help. To get to the relays, remove the fuse cover, then remove the screws holding the rear portion of the cover.
- The seat relay is powered by a 16A fuse (#2) via a diode with the ACC on, or it is powered through a 8A fuse (#9) via the door switches.
- Mechanical relays like these will click noticeably - so listen carefully while someone operates the seat switch with door open or ignition on. You can also check the relay for certain by removing it and measuring resistance across the input pins, and if that is OK check the output contacts by putting +/- 12v on the input pins while checking continuity on the output pins. Or, just get a new relay from the dealer if you are not comfortable with a Volt/Ohm meter :^)
- The relay (if working), sends high current to the seat motors via two 25A fuses (F and E). So there is a possibility these fuses are out. btw I do not think the two fuses are left and right seats, but rather for the different motors.
- From these fuses the power goes to the seat switches and the driver-seat memory unit.
The only connection I can think of between the overhead light and the seat relay is that they both are powered by the same fuse (#9) via the door switches. If fuse #2 and fuse #9 were both out, the seats would not work and the light would not work.
The only way I know to "manually" operate the passenger seat back is to pull the seat switch or the plug under the seat, and put +/- 12v across the gray and orange wires. Seat back direction depends on which wires you put the + and - 12v on. This is not hard if you are comfortable with electricity and can double check yourself.
Scott D

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It is important to note that fuses in these cars are notorious for developing very slight oxidization on the tips that fit into the small holes of the fuse holder. The fuse may look good but still not pass current. So remove the fuse and either replace it or clean the tips with fine sandpaper.
Some auto part stores have glass enclosed fuses with stainless ends that are very nice replacements!
Scott D

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Scott D wrote:

If you can't find those, at least buy replacement fuese which are copper alloy (golden), rather than the tin alloy (silvery) ones, which turn powdery and develop hairline cracks.
Swapped all of mine in the 123 and 124 and have not had any problems.
Cheers, WS
--
Change to leews to mail.

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correction to my "check by ear" relay test: it should click when the front door is opened or when the key is switched on. Check/replace fuses #2 and #9 first though.
Scott D
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