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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,386 Posts
Discussion Starter #1
This is a nagging problem that I can't find much info on. My overhead seat belt light seems to have a mind of its own. We always wear our seat belts....and this light flashes at random, pretty much the whole length of any drive. It almost seems like it's trying to give me an error code of its own.:rolleyes:

I don't know if they are related, but the passenger mirror light is very dim now, if at all. I've tried new bulbs and checked out the little switch-I've always figured it to be some sort of wiring problem upstream of the mirror. Unless they are related, I'd rather try to trace down the problem with the seat belt light for now. Any tips/ideas?

Kevin
 

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89 300E; 00 E320
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2,515 Posts
Complicated circuits
Red/White hot wire from fuse 9 and Red/Violet hot wire from fuse 5 go to E15/2 for fasten seatbelt and then leaves there on Brown/Red going to vanity lamps.
And then there is the Brown/Grey wire from the warning module that also goes to E15/2; but first that circuit has power from fuse 5 (Black/Red/Violet hot wire) and 9 (Red/White and Red/Green hot wire) as well with a warning buzzer switch and a few connections along the way. And at least a couple of grounds W12 and W4.

Here are the diagrams:

Warning System 135-4

N2/4 Warning module (seat belts, keys, lights) Behind right side of instrument cluster 240-4

S8/2 Warning buzzer contact, exterior lamps/central locking system Part of S2/1, S2/2 234-1

E15/2 Front dome lamp with shutoff delay and reading lamp Center of windshield header


X42 Connector, anti-theft alarm, frontfrear Beneath passengers footrest 244-3

X34 Connector, right front door contact switch In right front door jamb 246-2

W12 Ground, center console Behind lower front of console 240-2

Lamps: -Courtesy 128-9

-Vanity 129-4

W4 Ground, front dome lamp Center of windshield header, above front dome lamp 235-1
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,386 Posts
Discussion Starter #3
Thanks for all the diagrams...it's more complicated than I expected. They're all interconnected to a certain point....I'm not seeing a sensor/controller for the seat belt light that would act up and not cause something else to give signs. I'll print these off and see if I can figure out a logical route....thanks again.

Kevin
 

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"Gretchen" my 1986 300E 286000 km+ (RIP) August 2015
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1,092 Posts
As a temporary fix I'd cover it with electrical tape. Good Luck with the deciphering.
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,386 Posts
Discussion Starter #5
If it comes down to it, I'll just go back into the overhead and remove the bulb. I hate doing that though without a 'fix'...I've already disconnected the alarm system because of a bad micro-switch in the driver's door. That's not a high priority, but the nagging seat belt light is causing passengers to ask WTF.

Kevin
 

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About a dozen 1988, 1989, 1990, and 1991 sedans, wagons, 4Matics and 1 coupe
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5,466 Posts
Bulbs.
And good luck.
That overhead lamp/warning assembly is a PITA. There's more going on in there than you might think. ICs.
I think all three seatbelt warning lamps are controlled as a set using input from the warning chime module behind the cluster. The module grounds a signal line to the lamp assembly and then the ICs control a transistor to operate the warning lamps. The IC could be bad.
And getting to the the lamps (3) pretty much guarantees breaking some tabs that hold things together. BTDT You're better off getting a junkyard donor overhead assembly and trying that.
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
Joined
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10,386 Posts
Discussion Starter #7
Bulbs.
And good luck.
That overhead lamp/warning assembly is a PITA. There's more going on in there than you might think. ICs.
I think all three seatbelt warning lamps are controlled as a set using input from the warning chime module behind the cluster. The module grounds a signal line to the lamp assembly and then the ICs control a transistor to operate the warning lamps. The IC could be bad.
And getting to the the lamps (3) pretty much guarantees breaking some tabs that hold things together. BTDT You're better off getting a junkyard donor overhead assembly and trying that.
Absolutely correct....I've had that overhead out a couple of times;once to clean the cabin temp sensor and another time to replace a bulb. It IS very complicated and has its own PCB with IC's. I bet you're correct...it's probably a faulty IC...thanks for the idea! Best thing there I'm sure, is to find a junker and swap. As careful as I was, I broke off some tabs on that unit....it's almost impossible not to and especially with the plastic now brittle-common problem found throughout the car these days. :(

Kevin
 
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