PeachParts Mercedes-Benz Forum

PeachParts Mercedes-Benz Forum (
-   Tech Help (
-   -   Fuel Relay (

mpagnani 10-07-2002 01:52 PM

Fuel Relay

I read that some people used to make a bridge when the fuel relay is "dead" between some connection.

They told about pin #7 and #8 (hope) but I had a look on my relay and of course these number are not there !!!!

I would like to know what is behind these numbers/letters I found on the back of my relay:


where is the 12v input and where are the relay contact and . . . .

Just to be abble to make a bridge if I need to do it. (knowing that the best way is to have one spare relay)


mpagnani 10-09-2002 03:11 AM


John F 10-09-2002 09:07 AM

Fuel Pump Relay
With a cheap soldering gun, you can do a permanent fix on the relay.
The cover on the relay pops off. You'll find two solenoids, on the bottom near the pins.
The LARGER of the two is your fuel pump relay. Over the years the vibaration on the support(ground) piece has cracked the solder joint.
With a little flux and a hot solder gun/ solder, re-solder that joint on the back side.
Be careful not to solder adjacent circuits together. ZAP!!
Put the cover back on.
I did my '85 500SEC this way. Much better than a jump.
Good luck. Regards, John F

woody 10-09-2002 09:26 AM

Where were you the other day when I was having this problem?
I finally made a bridge to solve my fuel pump relay problem. The #& and #8 pins, to which you refer, are the female sockets on the fuse box that relay snaps into. AS you look toward the rear of the car, they are the last two that the relay snaps into side by side. If you take a paper clip and make a jumper, you will power the fuel pump continuously. that's 7 and 8.

mpagnani 10-09-2002 10:09 AM

need more precision
1 Attachment(s)
thank you John F
thank you woody

I realy apreciated your answers.

But I am not clear yet on where the connection is to do.

Here I tried to attach a drawing of what I have discovered till now.

the green spots are the holes in the connector (after the battery)
and the red texts are those I found on the back of my relay.

Now the question is : between wich letters is the bridge to do ?


woody 10-09-2002 10:46 AM

Jump E and H together with a paper clip, they are 7 and 8. Fuel pump should start up and run.

pentoman 10-09-2002 11:12 AM

Yes.. I did this but don't remember if it was these pins. I expect woody is right though. Make sure no live wires contact your ECU or ABS ECU, that happened to me and I had to replace the ABS ECU $$

Mick J 10-09-2002 04:41 PM

15 is the power feed from the ignition switch and TD is the run signal (and tachometer signal) from the igntion ECU. If you jump them you'll probably fry the ECU.

Try jumping 30 (permanent live feed from battery) to 87 which feeds to the pump(s) and heated lambda sensor - that's what happens inside the relay. If you want ignition switch control over the thing use 15 instead of 30 but that circuit is not designed to provide the current drawn by the pump(s) (that's one of the reasons for having a relay!). The wires to terminals 30 and 87 are 2.5mm whereas the wire at 15 is only 0.75mm.

Other terminals are

87v - feed to cold start valve
31 - ground
50 - feed from starter switch to run pump before engine running signal from ignition takes over
TF - not sure, it is connected to the fuel ECU

mpagnani 10-10-2002 02:52 AM

Thank you Mick J

For the complete explanation for those conections.

Yesterday I had the opportunity to speak with an MB technician. I told me about an more hole situated between 30 (D) and 87 (I) preventing the mismounting of the relay.

And he also told me to jump the contact of each side of this hole (30 & 87) to have the pump functionning all the time.

And I totaly agree with you concerning the pins to use.

I just want to make this brigde to ensure that is (or is not) this relay the cause of my problem.

Thanks again

All times are GMT -4. The time now is 08:42 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website