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Old 06-16-2000, 12:09 PM
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I have several questions from looking at the schematic on the CD form Mercedes. I was hoping that the starter relay was bad but not sure which of the three relays in the fuse box it is. I believe that it is the A/C Starter Relay towards the from of the vehicle. Although the problem I have is with the ignition off the relay seems to be feed by the battery bus not the start run bus. I have not finished investigating the wiring to see if there is an open wire somewhere. I was able to pull the relay out far enough and use a volt meter to determine that the relay is working properly. This also says that starter lockout switch is working fine too. The thing I am puzzled about is the schematic on the CD. It shows three relays but only give information about two. The relay towards the front of the car in the fuse box is called the A/C Starter Relay. The relay towards the back of the car in the fuse box is called the Fuel pump relay. It is the relay in the middle that it does not tell what it is used for. I am trying to make sure I have the right relay without having to do a bunch of wire tracing. Please someone help!!! If you have any suggestions on what could be causing the pull in coil from not getting voltage please let me know. We were able to jump voltage from the starter to the pull in coil and start the car.
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Old 06-16-2000, 10:43 PM
Registered User
Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
Some of these cars had a crazy thing where you had to be sitting in the seat or something to that effect?? I don't know, I'd have to look in the ETM.

Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
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Old 06-17-2000, 11:23 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The seat belt interlock relay wouldn't interfere with starting after 1975; in normal operation. During 1974 one had to buckle up to get the car started....that went over like a lead balloon and was changed the next year on almost all cars. Many of those systems had the seat sensor disconnected, which worked fine for decades. I still run across a 74 every year or two that the control unit fails after waiting for someone to sit in that seat. Most current techs never knew the possibility for a restrained start existed.

I had a car with an intermittant "no start". I drove and started the car for days (probably replaced the N/S switch) and could never get it to act up. Finally one day a customer called needing a ride and I went to pick him up with the car. When we were inside the car it wouldn't start. Luckily I put two and two together and had him get out of the car. It started right up. Come to find out that the car had the seat upholstered and they had reconnected the long ago disconnected passenger seat sensor. When ever someone sat in the passenger seat (and didn't buckle up) the car wouldn't start; just as it was supposed to do....

On a 78 model the seat belt interlock relay still probably had the start circuit running through it (I would have to look at a diagram). If you are in the CD go to the chassis section in group 54 or 82 and find seat belt interlock system. There were many versions.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

[This message has been edited by stevebfl (edited 06-17-2000).]
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Old 06-17-2000, 12:38 PM
Posts: n/a
Thanks for the infomation. According to the schematics there is not seat belt interlock. I am having problems making sure which of the three relays in the fuse are which? Does anyone know that answer.
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