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  #1  
Old 05-24-2011, 04:40 PM
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Annoying but Trivial Problem

My seat belt light keeps cycling through its routine even after the car is running and belts are worn correctly. It acts as if power had been dropped, then restored and it stays lit for about the same amount of time as it would normally. It comes on while driving. As long as the seat belt us being worn, just the light comes on. Unhook the seat belt and the light and buzzer come on. After 45 mins of driving all this stops and things work normally. What relay or wiring should I check? Seat belt buckle switch seems ok since it will stop the buzzing as soon as belt is buckled. Ignition switch problems? I've jiggled the key while this was going on but nothing changed. Is the buzzer the same one that goes on if you leave the key in the ignition?
My tach just sprang back to life after being out for over a month so I do think I've got electrical issues.
85 300DT 182000.
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1985 300D 197K - Semi-Daily Driver Diesel
1998 Volvo V70 AWD 226K - Daily Driver 2
1998 Volvo S70 140K - Wife's DD
2003 GMC Sonoma ZR2 Option - Rusty Truck
THE BABY 1958 220S Sedan 66K All original, never restored and never will be.
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  #2  
Old 05-24-2011, 09:22 PM
compu_85's Avatar
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Check the grounds for the instrument cluster.

-J
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1991 350SDL. 230,000 miles (new motor @ 150,000).

2013 Fiat 500E. 20,000 miles, 80 miles at a time.
2012 Passat TDI. 95,000 miles. More space, power, and fuel economy than the Benz
2004 Touareg V10 TDI. 150,000 miles. One of 450.
1999 Jetta TDI. 310,000 miles.
1992 Jetta ECOdiesel. 156,000 miles. 1 of 48. Sold.
1991 Jetta ECOdiesel. 430,000 miles. 1 of 700. Sold to VeeDubTDI, totaled in front of our house
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  #3  
Old 05-24-2011, 09:49 PM
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Unplug it under the seat.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #4  
Old 05-24-2011, 09:54 PM
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Quote:
Originally Posted by kerry View Post
Unplug it under the seat.
That won't keep the light from going off over and over, plus being an 85 that might disable the seatbelt tensioners.

-J
__________________
1991 350SDL. 230,000 miles (new motor @ 150,000).

2013 Fiat 500E. 20,000 miles, 80 miles at a time.
2012 Passat TDI. 95,000 miles. More space, power, and fuel economy than the Benz
2004 Touareg V10 TDI. 150,000 miles. One of 450.
1999 Jetta TDI. 310,000 miles.
1992 Jetta ECOdiesel. 156,000 miles. 1 of 48. Sold.
1991 Jetta ECOdiesel. 430,000 miles. 1 of 700. Sold to VeeDubTDI, totaled in front of our house
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  #5  
Old 05-24-2011, 10:10 PM
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Quote:
Originally Posted by compu_85 View Post
plus being an 85 that might disable the seatbelt tensioners.

-J
Can you elaborate on that? I've got an 85 with the wires unplugged. Am I going to die in an accident? I thought the tensioners were mechanical.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #6  
Old 05-24-2011, 10:52 PM
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I have a similar (but not quite the same problem) in the 240d.
just curious, when the light is on, if you pull the e-brake release, does the light go off?
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  #7  
Old 05-24-2011, 11:49 PM
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Quote:
Originally Posted by zeke View Post
I have a similar (but not quite the same problem) in the 240d.
just curious, when the light is on, if you pull the e-brake release, does the light go off?
Nope. Thought of that too. Didn't do anything.
__________________
1985 300D 197K - Semi-Daily Driver Diesel
1998 Volvo V70 AWD 226K - Daily Driver 2
1998 Volvo S70 140K - Wife's DD
2003 GMC Sonoma ZR2 Option - Rusty Truck
THE BABY 1958 220S Sedan 66K All original, never restored and never will be.
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  #8  
Old 05-24-2011, 11:51 PM
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Join Date: Apr 2002
Location: RI
Posts: 1,040
Inst panel grounds. If I pop out the cluster, will it be obvious where the grounds are? Any way to enhance the grounding of the cluster?
__________________
1985 300D 197K - Semi-Daily Driver Diesel
1998 Volvo V70 AWD 226K - Daily Driver 2
1998 Volvo S70 140K - Wife's DD
2003 GMC Sonoma ZR2 Option - Rusty Truck
THE BABY 1958 220S Sedan 66K All original, never restored and never will be.
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  #9  
Old 05-25-2011, 12:43 AM
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Location: Lexington, NC or Boone, NC
Posts: 2,268
Check all your fuses, I've seen a cracked fuse cause something like this before. One time in my 300SDL (has a different system; the seat belt light is up on the roof near the sunroof switch and the dome light) one of the "door sill lights" got slammed in the back door, causing the thing to short out the light bulb contact to the car's body; instant fuse blow. Dashboard instruments went dead, including speedo, tach, everything... and the seat belt thing wouldn't quit flashing. When I changed the fuse (after correcting the problem with the slammed light), in addition to the instruments working again, the seat belt light returned to normal operation.

300SD has different wiring; different fuses control different sets of things. But it's worth a quick browse through the fusebox.
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"What could possibly go wrong?"

~Michael S.~ -
1986 M-B 300SDL, retired due to rust and electrical problems. Donated engine to:
1987 M-B 300SDL, odo dead. New project.
1982 M-B 240D, odo stopped at 308,000
1982 M-B 300SD, 175,000
1989 Dodge Ramcharger, 87,000 - 4wd, 318
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  #10  
Old 05-25-2011, 07:23 AM
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Waiting for his Model 3..
 
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Location: Springfield VA
Posts: 5,174
Quote:
Originally Posted by kerry View Post
Can you elaborate on that? I've got an 85 with the wires unplugged. Am I going to die in an accident? I thought the tensioners were mechanical.
All 1985 and later models have emergency tensioning retractors for both front seats. In a crash the control unit in front of the shifter deploys the retractors, which snap the belts back and take out any slack, so they can catch you right away and won't "pay out" as much as you pull on the belt. A very good feature, and I believe MB was the first to use it.

-J
__________________
1991 350SDL. 230,000 miles (new motor @ 150,000).

2013 Fiat 500E. 20,000 miles, 80 miles at a time.
2012 Passat TDI. 95,000 miles. More space, power, and fuel economy than the Benz
2004 Touareg V10 TDI. 150,000 miles. One of 450.
1999 Jetta TDI. 310,000 miles.
1992 Jetta ECOdiesel. 156,000 miles. 1 of 48. Sold.
1991 Jetta ECOdiesel. 430,000 miles. 1 of 700. Sold to VeeDubTDI, totaled in front of our house
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