280SL (W113) weird electrical gremlin - Mercedes-Benz Forum

 
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post #1 of 5 (permalink) Old 05-07-2009, 03:19 PM Thread Starter
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280SL (W113) weird electrical gremlin

So, it's been damp in the garage recently - a little more then usual. I've been driving the SL on and off for about a month with no problems (or, at least no problems worth mentioning for a 35 year old car).

It was super nice this morning so I wanted to drive it to get coffee. I removed the battery tender, opened the drivers door and <bang> on comes half the idiot lights on the dash, the fuel gauge moves to full (yes, tank is full) and I hear the fuel pump start...WTH ???

Closing the door sends everything back to normal. Uh-Oh, thinks I, a ground problem...

After starting it up (normally), the charge light (alternator light) stays on and the ignition switch won't shut off the engine with the door open - it'll run with the key OUT until you close the drivers door.

Now, I'm not a stranger to funky auto electrical problems since I own a couple of old ALFA's too. I'm assuming the problem has to do with the dampness and it'll probably "correct" itself when it dries out. BUT, I would like to fix the underlying problem. I haven't found my wiring diagram yet and I have NOT searched the forum like a good boy BUT, has anybody seen anything like this before so I can focus on the proper circuits ? I'm guessing a faulty ground related to the ignition switch and the small amount of current flowing when the door is opened (courtesy light) is freaking something out.

1978 Mog 416.141 DoKa
1971 W113 280SL
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..the road to nowhere. . .leads to me.
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post #2 of 5 (permalink) Old 05-07-2009, 03:48 PM Thread Starter
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Well, that didn't take too long to figure out (hopefully). Here's the link in case other W113 owners have the same problem.

Pagoda SL Group Technical Manual :: Brake / LowFluidWarningLight

Executive Summary: When both the 'door ajar' AND 'low brake fluid' warnings are triggered at the same time, two DC circuits which MUST remain isolated are connected together, resulting in much weirdness and "fun".

My brake fluid was low a few weeks ago and I refilled it. That sensor must be acting up now. It's fun to find all the crazy problems caused by "legislation"...

I'll proceed like it IS the brake fluid level switch and report back when the problem is fixed. Thank God it's probably NOT a ground problem

1978 Mog 416.141 DoKa
1971 W113 280SL
_______________
..the road to nowhere. . .leads to me.

Last edited by Mogasaurus; 05-07-2009 at 03:53 PM.
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post #3 of 5 (permalink) Old 05-10-2009, 05:26 AM
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That's one I've never heard of, but glad you found out the problem! Any rodents in your garage? I was thinking one might have made a meal of your wiring harness.
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post #4 of 5 (permalink) Old 05-11-2009, 09:39 AM Thread Starter
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Yes, that would be a stumper without the knowledge. I'm sure "back in the day" every Benz mechanic had a service bulletin taped to the wall describing it.

My problem was low brake fluid in the rear reservoir triggering the fault light. When the door was opened, it did exactly what that Pagoda Group wiki entry said would happen. The question is now, how did the brake fluid GET low since I just filled it ? There is no indication of a leak so I guess I wait to see what happens in the next week or so...

1978 Mog 416.141 DoKa
1971 W113 280SL
_______________
..the road to nowhere. . .leads to me.
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post #5 of 5 (permalink) Old 05-16-2009, 10:47 AM
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Low brake fluid and no sign of a leak? The master cylinder is bad,the fluid is getting sucked into the brake booster.Suck the fluid out when the cylinder is off.Put a new one on,don't get a rebuilt or try to fix it.
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