Seatbelt/Brake Relay Questions

[Superman]

Consider the pictures below. Behind the far left gauge I see a relay is possibly missing. I am having trouble with my Brake/Seatbelt dash light, and I am also having trouble with my rev limiter. Here are my questions:

1) Is this where the Brake/ Seat Belt relay should be?
2) Does this relay also involve the rev limiter?
3) What is the part number of this relay (If you know it. I have a bag of relays)?

[FrankM_]

Hi,

in my 1985 model, the seatbelt relay is 91161810200 and it is located behind the second gauge from the left, in a double socket (there is another relay right next to it, I believe the relay for the electric window motors 'Fensterheber' ? - see photo).
This relay actually does not switch anything on/off except itself and creates the 'buzzing' noise that way.

The Red/BLACK (RT/SW) cable is the +12V and also connects through to the warning light block, the 'L' output controls the seatbelt warning lamp (GRN/YEL). The electronics look like a simple delay circuit.
The other lights in the warning light block are controlled by the handbreak switch and the continuous circuit through the 4 brakepad wear sensors.

This relay has NOTHING to do with the rev limiter, that is a set value in your Motronic EPROM chip. If you have an aftermarket chip, they often set the revlimiter to a higher value (you can use TunerPro and an EPROM writer to read the chip / change value / write new chip).

[Superman]

I started several threads here with multiple questions and various replies which I appreciated. My system is now working fine, or so it seems. In one thread I asked about how the Brake/Seat Belt light is supposed to work and never got clarity on that. Here is my report on how this light should work on an SC. First, here is the passage from the Owners Manual:



The Seat Belt light comes on for a bit, maybe fifteen seconds, then goes off. Whether the seat belts are fastened or not. I am not aware of any electrical connections at the seat belts, telling the system whether the belts are fastened or not. I am also not aware of any buzzers. I have not heard buzzers, ever. This is my third SC.

The Brake light turns on when the key is turned, and will not go off while the key is turned but the engine is off. Whether or not the park brake is applied. Once the engine is started, this light will go off when the park brake is released. Presumably, the light will illuminate if the regular braking system has a malfunction (as mentioned in the owner's manual).

The lamps are easily replaceable, without soldering. They use the same tiny bulb as the defroster light which is under the park brake handle.

This concludes my report.

[FrankM_]

Thanks for the copy of the manual on how it should work !

What part number is on your seatbelt relay ?

On the schematic above, the contact switch on the right is integrated in the seatbelt receptacle on the 84-88 Carrera.

[proporsche]

i have several of these relays with different year marking...part number
911 618 102 00

Ivan

[FrankM_]

If I look at the '82 schema for the SC, I can see that it also includes the switch at the driver's side seatbelt receptacle, so that should be there.



Once you insert the seatbelt (before or after contact), the seatbelt light should not light up. If it is not inserted and your contact is on the two transistor circuit with a capacitor charging over the variable resistor makes the delay that keeps the seatbelt warning light on for a certain amount of time. Adjustable by moving the potentiometer inside the relay.
In my MY85, when the seatbelt is not inserted, the relay that switches itself on/off is used to create a buzzing sound. Maybe that is different in the SC version ?