[W126 Coupe] Fuel pump relay jumper

Gerry Van Zandt gerryvz at me.com
Tue Aug 9 12:33:14 EDT 2011


It's pins #7 and #8, which are adjacent to each other. Get a piece of heavy gauge wire, about 1.5-2 inches long, and bend it into a "U" shape. Twist the ends and then you can insert it into these pins.

This is only suitable for temporary testing and diagnostic purposes -- not as a replacement for a non-functioning fuel pump relay. In an extreme pinch, you could use this jumper to get you home if your FPR fails on the road, but I'd only drive a very limited distance with it (perhaps 5 miles or so). Better to just have a spare FPR on hand in your emergency kit in the trunk, because without a functional FPR, you're pretty much dead in the water.

The purpose of jumping these two pins is to take the ignition (key) out of the picture for operating the fuel pumps. When you jump these two pins, you should hear your fuel pumps in the rear "whirr" (come to life) and begin supplying fuel to the engine. This capability was invaluable recently when I had to diagnose my failed fuel pumps on my 560SEC (the E10 fuel we are saddled with is a 126 fuel pump killer over time and mileage). The fact that when I jumpered these pins, and didn't hear my pumps come to life, indicated that they were dead. Tapping them with a wrench brought them back to life, but it was clear they were bad (they did have a 120K mile life, and had been good since 1996 when they were installed, so I can't complain too much).

In short, the jumper can help eliminate fuel delivery as a problem for a non-starting car, or it can get you home in an extreme pinch. Be warned though, the wire gets HOT when jumpering and I don't think this is safe except as a stop-gap measure.

Cheers,
Gerry



On Aug 9, 2011, at 11:15 AM, mbcoupes-request at mbcoupes.com wrote:


> Message: 1

> Date: Mon, 8 Aug 2011 17:53:39 +0000

> From: Mister McGoo <eelploot at hotmail.com>

> Subject: [W126 Coupe] Fuel pump relay jumper

> To: MB COUPES <mbcoupes at mbcoupes.com>

> Message-ID: <SNT123-W5030E93B16A03A1D4D82ECCB210 at phx.gbl>

> Content-Type: text/plain; charset="iso-8859-1"

>

>

> Hi, all. Need to know the pin No's to jump for fuel pump relay '88 560. -Bellamy


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