97 Mercedes C280, Viper 560xv

Hi guys,

I have opened up the driver side door pannel to make sure the wires are the same in the drivers's kick pannel, also I checked the same at the back of trunk lid and found that there are 3 wires, blue, black and brown that are connected to the key cylinders.

With digital meter, I probe the blue wire and shows Positive 11.70V for locking and unlocking, I then checked black wire and it shows 11.60V or so for locking and unlocking.

I am confused, it should show zero voltage either locking or unlocking but my wires shows constant 12 volts all the time. Am I doing something wrong ?

My car is Mercedes C280(W202), 1997.My car is equipped with original keyless with switch blade key

Any help would be greatly appreciated.

Thanks

infinkc, there are Two female connectors connected to the main vacum pump located in the rear corner of trunk.

Smaller connector has 3 wires :Brown Grey/Blue Yellow/BlackBlue                                      

Bigger connector has 7wires:Brown BROWN / Brown BROWN / Brown BROWN / Red Grey/Green WHITE/ Black Yellow / YELLOW Blue

I don't see purple Brown wire at the pump, all the wires above are connected to the original manufactured keyless module. Ther are too many wires from that module but some go to the trunk lid key cylinder, drivers key cylinder, central locking button on the center of dash. The method of probing wires are;

1. Open the back of carpeted trunk lid, found the key cylinder and found 3 wires, one is brown(ground), Blue and black, I have tested each wire(Blue, black) by probing plus and ground to the chasis, then with keyless switch blade lock and unlock.Both wires showed constant voltage for lock and unlock

2. I did the same for the front driver side door(there are same color of wires as in the trunk lid), result is the same as #1 above.

Should I check the wires between the keyless module and the main pump(rear corner in the trunk)? to get zero voltage when locking?

Any info will be greatly appreciated, thanks guys

Hi guys, I have been doing research on door locks, checking with DOOR LOCK on left, in the car security and relays as well. What's confusing with me is that my car does not seem to correspond with the diagram shown in the relay shown in the vacum for mercedes.

If my car correspond to single polarity that changes locks, unlocks then I have no problem but my car has Black wire for Lock(-) and Blue for Unlock(-), How should I connect these wires to the 451M? Should I cut either black or blue wires from the car and connect the end to which wires of 451M ?

My car is C280(W202), 1997 with switchbalde key

Thank you guys for any help in advance

MO,yes it is negative pulse. In the DOOR LOCK on left in the Car Security there is diagram for vacum pump(not for the single polarity) it says that either 451M or two relays are needed.

Are you saying that i do not need 451M or relays ?, the reason for choosing 451M is that it may be easier and compact(small) in size.

thanks for your advise