Seatbelt light turning on and off - Mercedes-Benz Forum
 
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post #1 of 8 (permalink) Old 02-09-2016, 04:25 AM Thread Starter
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Seatbelt light turning on and off

Hello All,
I have an '82 280SE Euro and there are (2) scenarios with my seat belt light on the cluster that keeps turning on and off.

Scenario 1:
Start the car, engine is running , headlights are off, seat belt light is on. Once I start driving then the seat belt light turns off.

Scenario 2:
While driving with the headlights on, the seat belt light stays on solid and turns off once I accelerate above 3000 rpm.

The only thing I did recently was replace the alternator and made sure the ground is secured.

Any clue what is causing this?

Irving, TX
2003 CL500 (Sold)
2008 CLS550
1982 280 SE (Grey Market)
2012 Toyota Corolla S
1996 Corvette (LT1 w/ LT4 hotcam)

Last edited by dfwcl500; 02-09-2016 at 04:27 AM.
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post #2 of 8 (permalink) Old 02-09-2016, 05:18 AM
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Many seat belt warning systems are timed based on alternator output; when the alternator comes on line the seat belt warning starts its cycle to off. If your new alternator output is not consistent it may be triggering the seat belt warning system at unexpected times. You could drive with a volt meter attached to the alternator and see if the changes in the light coincide with voltage fluctuations.

Or, recheck the alternator installation.

Re-read your scenarios. It sounds like the alternator isn't keeping up with the load at low RPM's. Adding the headlights increases the load and delays the point where the alternator meets the load requirements. My WAG is the alternator has a bad phase or diode.
carnut62 and liviu165 like this.

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post #3 of 8 (permalink) Old 02-09-2016, 05:36 AM
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another consideration on G1 cars, is to disconnect the battery. Pull cluster and add a ground wire to the metal side of the cluster and make it long enough to attach to the ground block behind the cluster but with enough slack to remove cluster.


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post #4 of 8 (permalink) Old 02-09-2016, 06:20 AM Thread Starter
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Originally Posted by 281lxm View Post
another consideration on G1 cars, is to disconnect the battery. Pull cluster and add a ground wire to the metal side of the cluster and make it long enough to attach to the ground block behind the cluster but with enough slack to remove cluster.
Come to think of it, it does sound like a runaway leaking circuit without a proper ground. Could it be a faulty FACON 2022 capacitor that plugs into the alternator to clamp down the circuit from having a leaking voltage to other components? because I reused the old capacitor and just installed it on the new alternator.

If not, I'll try to just solder a ground line on the cluster and just tap screw it to the chassis.

Irving, TX
2003 CL500 (Sold)
2008 CLS550
1982 280 SE (Grey Market)
2012 Toyota Corolla S
1996 Corvette (LT1 w/ LT4 hotcam)
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post #5 of 8 (permalink) Old 02-09-2016, 08:22 AM
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Or...the switch in the seatbelt receiver beside the seat is dirty / wonky (technical term!). Stuff some rags around the receiver and spray the internals with contact cleaner / WD40, then plug/unplug the seatbelt a couple dozen times.

Blasphemous Mike
US '87 560SEC with Euro headlights, clear markers, H&Rs, 17x8.5/Nitto's, ATE slotted rotors with ceramic pads, BergWerks FGS, 3.07 Limited Slip. '87 560SEL with Euro Headlights, lowered, 235/40/17's
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post #6 of 8 (permalink) Old 02-09-2016, 11:15 AM Thread Starter
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Problem solved. the problem was the wiring behind the instrument cluster, the existing contact wasn't making a good ground. Thanks again 281lxm. These 1st Gen w126's can be tricky.

Irving, TX
2003 CL500 (Sold)
2008 CLS550
1982 280 SE (Grey Market)
2012 Toyota Corolla S
1996 Corvette (LT1 w/ LT4 hotcam)
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post #7 of 8 (permalink) Old 02-09-2016, 01:41 PM
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WINNER WINNER CHICKEN DINNER! That helps a lot when this crap gets fixed (kite string and peanut butter not required).

@mramay that is a great thing for everyone to do. One cannot believe the accumulated @%)%%$$%& inside the female end of that unit, let alone the end of the combination switch...UGH it gets pretty gross.


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post #8 of 8 (permalink) Old 02-09-2016, 06:55 PM
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Glad it turned out to be simple/cheap!

John
"Real engines don't have spark plugs!"
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