does my 1987 560sl have a seat sensor for an airbag?
 

If so, how can I do a check to see if this has gone bad and causing my srs light to go on?
Kimmy

No, you do not have one.

Voltage below 10.1vDC will trigger the SRS light, check the alternator output. Also dirty contacts or worn slip rings can trigger the light. You really didn't give much info on your SRS light problem - does it not go out after start up or does it come on while driving?

SRS lights can also be caused by a bad switch in the seat belt latch.

OK, Here is the history, the car has been maintain perfectly from day one. Never any problems. It only has 60k miles on it. One owner, (my mother) and now me. So I get this great car and about 1 month later It doesn't start. I'm thinkin that it has been sitting too long, so I take it on a long drive and park it again. Same thing. So I buy a new battery. I put it in and suddenly the SRS light is on every time I start it and stays on until I shut it off. Next time I go to start it. It is dead dead dead. NOTHING AT ALL So I jump it and drove to the shop, after many hours of who knows what and lots of $$$$$ I learn that I have a "draw on the battery" he said he thinks its the clock and wants to replace it. After learning how much that was going to cost I told him to just disconnect it. I left thinking it was fixed and drive away. Next time I try to start it, NOTHING. I am so sad at this point I can't even stand to look at her. I tried to put a child into the trunk to see if the light was staying on. That was a big no. So that's the whole bannana. Any thoughts now. or are ya sorry ya asked LOL. One more tid bit, (for whatever it's worth) the gas gauge began to go a little crazy just as this whole thing started to happen, ya know bouncing back and forth, shakey like sometimes. And that's my story and I'm stickin to it.
Kimmy
Kimmy

It is probably one of the first things your mechanic checked, but is your alternator charging?

Your gas gauge problem is surely the sending unit. They are a not infrequent failure item.

OK, so now you need to take your DMM (digital multi meter, or regular multi meter) and see what kind of charging out put your alternator has. With the engine running your should be seeing 13.8 vDC or so. It does sound like your alternator isn't charging the battery. Could be corroded terminals or a bad regulator (try a search on alternator brushes). Replacing the voltage regulator isn't terribly difficult, but might be a tad tight in that V-8 engine bay. Remember, 10.1vDC or less will trigger the SRS light...and you keep having to jump it...sounds like you need to tend to the alternator.

Plus with all this jump starting you might start seeing the ABS MIL too. If the ABS lamp comes on be sure to check the 10 amp blade fuse on top of the OVP.

I'm no electrical wizard but can't you test the current being drawn from the battery with everything off and tell if there is a draw on the battery?

Once it is determined that there is a draw can fuses be pulled (one at a time) to isolate where the current draw is coming from?

Mike, I really appreciate you helping me through this, everyone else seems to give up about here. I know it's not the alternator and the terminals are showroom shiny. I am embarassed to tell you that I went and purchased a mulit tester "actron" is the name of the one I got. I have read the instruction 3x and still have no idea of how to use it. It has a dial and around it, several sections. I think I want the one that says DCV, but what number do I set it to? It also has 3 holes to plug a red and black wire into. I know I can do this, Please don't give up on me. I will wait to hear back from you on how to use this silly thing.
Kimm

I tried to do this at one point, but I'm not sure I knew how to set my tester. Too many choices on its dial. The numbers I was getting were all over the board. Plus it doesn't stay charged long enough for me to run the test. I drains that fast.

What do you mean when you say that my gas gauge is the sending unit? And yes the alternator was my first thought as well and it is good.

There is a chunk of pipe inserted into the top of your gas tank that holds a float that positions some sprung copper contacts down a wire. As the float moves with the level of the fuel, the resistance of the wire between the contacts and the end of the wire changes. The wires and contacts become gummed up and cause the resistance value to change erradically. This is why your fuel level needle jumps around. I removed my sending unit and tried to clean the wire and contacts to no avail. It lessened the jumping needle, but in the end, I will have to replace the sending unit just as you will.

OK, you'll want to put the red lead in the hole marked + and the black lead in the -. Set the dial to DCV to a number higher than 12, probably should be a setting for 20+/- DCV, that is the one you'll want. Before starting the car put the + lead on the + battery post and the - lead on the _ battery post, what is your reading? Should be 12.5vDC or so. Next start the car and repeat the test, what is the reading now? You should be seeing 13.8vDC or so.

Report back with your findings.

This is going to sound elementary but has the battery itself been tested? Once batteries are drained to nothing once they may not hold a charge.

I can find some old posts where a mechanic tested the alternator and it turned out to be bad.

I think we have some misdiagnosis here. It's the clock? Try pulling the fuse for the instrument cluster and seeing if that stops the key-off drain. That's a pretty simple thing to check and your mechanic's wish to just start replaing parts willy-nilly sets off alarms with me.

Getting back to the problem. The obvious needs to be checked: The alternator and voltage regulator. Too much voltage could be frying the battery. Many MB owners have been stumped by an alternator with a lower output that is still charging to some degree. Mechanic puts meter on posts, finds output, and declares charging system okay.

Once the charging problem is sorted, you may have to replace the battery as depp discharging can wreck even a farily new battery...