seat module draining battery overnight

 Hi all! I have a 2001 Mercedes 320 (not 4matic)  and my seat module drains my battery overnight. The module costs about $400 each and I have to change two. The connector consists Three wires (ground, constant,, and a wire that only gives power when the car is switched on.  In the MB forum, they said it is the constant power wire that causes the battery drain so they were suggesting I cut that and splice it to the wire that only turns on when the car is switched on. This is fine. The only thing I will be losing is the memory which is not really a problem since I am the only one using the car. I could do this procedure but I want to make sure this does not overload the wire I will splice it to and burn a fuse. Is there another way of solving this problem. Right now the seat is adjusted and the connectors are off so as not to drain the battery. I just plug it if I need to change seat and steering adjustments. Any help very much be appreciated.

THANK YOU GUYS!!!

draw could be from anything, highly doubt it would be your seat module that has been in the vehicle since new.Ted

2nd Year Tier 1 Medical School

Still installing as a hobby...pays for groceries

Compustar Expert

Thanks tedmon. Had no problem before this.  When this happened, I went to MB forum to find out what must be going on and they all pointed out to the seat module. For the meantime I was charging up my battery. The car started after the charge so I pulled out the seat module plug and used it for about 3 days and no battery drained happened and car was starting fine. Since I bought a charger and an emergency starter I plugged in the seat module when I got home in the afternoon and sure enough the car would not start the following morning. I then connect the emergency starter so the car started. used it for 2days and it was okay with the seat module plugged in. Friday afternoon I decided I would not use the car over the weekend and see if something happens with the seat module unplugged. Monday morning the car started fine.

Fist thing I would say is that it's probably a good idea to invest in a multimeter that can measure current draw. There should certainly be enough other websites (or probably/maybe even a tutorial on this site as to how to connect the meter to the car. Anyway, connect and set up the meter, and then check your readings with the seat module(s)plugged and unplugged and see if there's a major difference. As far as making the seat modules stay unconnected from constant power when the car is off, that should be pretty easy. The ignition power feed coming from the car may or may not be strong enough to power the seat module...hard to tell. You could always take your chances and do it and see if any fuses blow. But you can easily prevent any of that by installing a relay at the connector for each seat, as follows: 86: chassis ground of car 85: splice onto ignition wire going to seat module ---CUT THE CONSTANT WIRE THAT GOES TO THE SEAT MODULE IN HALF--- 87: car side of cut constant wire 87a: no connection 30: seat side of cut constant wire And now, after you do this, the constant wire will "pass" through the relay, but only when the ignition is on. And the seat will still be drawing power from the place that Mercedes intended. Also, after all these episodes of your battery going dead, don't forget to get it tested (after you've fixed the problem for good with the car). It will be no surprised if the battery has been damaged by now and might need to be replaced.

I suggest you use that meter to see if there's constant power on the ignition. That would be easy to reroute or even a faulty door trigger making the ignition "turn on" to power the seats. Also think about this, what are the odds of BOTH seat modules being faulty? On further thought if you can get your hands on diagnostic equipment that will give you a definite answer, my last guess would be a faulty SAM module (engine bay fusebox).

Thanks guys!!! Advise well taken. I will try it this weekend but no longer than Sunday noon since it's Superbowl Sunday. Is there a particular relay that I should look for when I go to the parts store. (brand, part no. and how many amps.) Thanks again!!!

Standard 4 pin Bosch/Tycho cube type. Please let us know if that did the trick.

Will do. Thanks all!!!

Which of course isn't the answer. Have you even considered doing those tests that Chris and I mentioned? Have you considered the odds against BOTH seat units developing this problem at once?