Fuel pump relay location

Tiny
CHAD COLLINS
  • MEMBER
  • 1996 MERCEDES BENZ 320E
  • AUTOMATIC
  • 150,000 MILES
I am desperately trying to find the location of my fuel pump relay on my car. I have looked all over the Internet and cannot find the right location. Several people have told me the same thing, but it is definitely not under my seat next to the battery. Only fuses are there. No relay. Please advise. Thank you
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Monday, November 28th, 2016 AT 8:54 PM

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Tiny
CARADIODOC
  • EXPERT
Any chance someone removed it and rewired the system so the pump runs all the time the ignition switch is on? I have read about that before. The clue would be you can hear the hum of the pump any time the ignition switch is on. That creates a major fire threat in a crash. If you hear the pump run for one second when you turn on the ignition switch, then it turns off until you start cranking the engine, the circuit is working properly.

Here is a diagram from Mitchell ProDemand. This is the only reference to the relay's location.
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Monday, November 28th, 2016 AT 10:14 PM
Tiny
CARADIODOC
  • EXPERT
Any chance your car is a late 1995 or early 1997 production? Those years could be different. Here, this first diagram is for a 1995, and the arrow is pointing at the driver's window, (I guess it should be intuitively obvious it is pointing to the rear seat). The written description again says "under the rear seat", but it makes no mention of being next to the battery.

For the 1997 model, there are two diagrams. The second one is quite different and is the second one posted here. The first diagram is identical to the previous one for the 1996 model. It is not clear if the 1997 uses the separate relay in the rear seat, the relay module up front, or both.
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Monday, November 28th, 2016 AT 10:32 PM
Tiny
KEN
  • ADMIN
Hello,

Here is more information

The fuel pump relay (K27) is switched by a ground signal from the control unit at terminal 86. If the contact is closed, the fuel pump (M3) is connected to terminal 30 (B+) via terminal 87. Circuit 30 is protected by a 30 A fuse.

With models 129, 140, 202, 208, the fuse is attached to the relay.

On vehicles with two fuel pumps, the pumps are connected in parallel.

The fuel pump relay is inside of the relay module.

(With diagrams below)

Please let us know what happens.

Cheers, Ken
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Thursday, November 16th, 2017 AT 11:37 AM

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