Fuel Pump Relay and pin locations? 280SE 1972 4.5L - Mercedes-Benz Forum
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#1 (permalink) Old 11-07-2006, 05:22 PM
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Fuel Pump Relay and pin locations? 280SE 1972 4.5L

Can anyone provide tips on how to test the fuel pump relay, and which relay under the hood it even is? I've looked at the fuses, and they all look ok. Somehow, I've suddenly lost the 12v at the fuel pump. nutZ4benZ had a link for steps to troubleshoot a Bosch fuel injection system, but I haven't been able to find out where all the pin locations are at that he refers to when he talks about jumpering across certain pins to test. The relay that I think controls the fuel pump does not have the same numbering scheme on it that he refers to.

I've tried searching though old posts, but haven't found where there is a link to the wiring diagram for this car. I have the German "catalog" of parts for this vehicle, but it only lists the numbers and does not give the part names or how they are wired together.

Thanks again for the helpful input!
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#2 (permalink) Old 11-07-2006, 05:24 PM
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If I remember right, the W108/109 cars have three round-looking relays on the passenger side of the firewall. One of them is the fuel pump relay. Swap them around to see if you get voltage at the pump.

Felicita e un bicchiere di vino con un panino.
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#3 (permalink) Old 11-08-2006, 07:41 AM
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From what I can tell, I have 1 relay that is mounted on the passenger side of the engine compartment behind the battery. I believe that is suppose to be the fuel pump relay. It is rectangular and has 5 pins (1 pin plugs into a empty slot). However, the part number on it is Bosch 332-202-001, but what I have found on-line for a replacement fuel pump relay calls for a Bosch 332-008-002 (also rectangular).

The 3 relays that are mounted side-by side in the engine compartment in front of the glove compartment have the outer 2 being round. The part number is 000-542-97-19. The middle one is square. It's part number is 001-542-02.

Could someone have substituted a different relay for my fuel pump, that might have worked but just had an extra pin function that wasn't used?
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#4 (permalink) Old 11-12-2006, 11:47 AM
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Still need help with relay & wiring

Fuel Pump Relay and pin locations? 280SE 1972 4.5L-relays-mercedes.jpg

I'm trying the picture attachment feature for the first time. Sorry to cut off a lot of the photo, but the upload feature had a file size limitation. In the lower left is the rectangular relay that was mounted to the passenger firewall. At the top of the photo are 3 more relays.

Does anyone know which relay should operate the fuel pump? I tried running a wire from the positive wire at the fuel pump back to these relays, but could not find zero resistance to any of the wires using a mutimeter.

I'm going to post another relay question as a separate thread. I hope someone out there has some insight they can provide. This is frustrating!
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#5 (permalink) Old 11-12-2006, 12:35 PM
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It is not a fuel pump relay. It is deemed a "change-over relay' and seems to be for A/C, electric windows, seat belt warning, and/or turn signal. Mercedes number is 000 542 5919.
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#6 (permalink) Old 11-12-2006, 02:36 PM
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Thank you for your input! I could not see how this could provide the 12V to the fuel pump. Any idea which relay might give voltage to the pump? Since none of the wires off of any of the other relays I checked showed continuity to the (+) at the pump, there must either be another device between the relay and the pump, or there is another relay/fuse somewhere that I haven't seen, or there is a break in the wire between the relay and the pump. Any suggestions?? And, do you know if there is a schematic/photo anywhere out there in the vast Internet that I can buy that shows the electrical layout for this vehicle?
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#7 (permalink) Old 11-12-2006, 02:52 PM
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Fuel Pump Relay: MB P/N: 000 542 8719; Bosch P/N: 0 332 008 002
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#8 (permalink) Old 11-12-2006, 03:43 PM
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Ron,

I trust ya, but where in the heck is this thing suppose to be??? The only relay I can find that is rectangular in shape is the one that was mounted behind the battery, but it's Bosch number is 332-202-001.
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#9 (permalink) Old 11-12-2006, 03:55 PM
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That's all I got -- do with it what you will.
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#10 (permalink) Old 11-12-2006, 05:25 PM
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my relay like ron has pictured is attached with another similar relay to the inner fender beside the battery, not behind it where you have the window fuses, etc.

One week ago I realized that I was not hearing the fuel pump energize and that simple item could be my non-start problem. I initally assumed all kinds of nasty, dire events. Instaed, all I did was spin the fuel pump fuse (left driver knee area) to clean off corrosion and -- VOILA-- a working, running 108! Do not remember the fuse number, hopefully, you still have the index inside the fuse box cover.

It would be nice if this is it....
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