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$1500 To Replace Fuel Pump Wiring Harness - 05 E55 In For Fuel Tank, Pumps, etc
Hey guys, my 05 E55 is at the dealership for the fuel tank, fuel pump, etc extended warranty. As I should have expected, there's always more to the story once the car is in shop being worked on. I get a call that the fuel pump wiring harness and fuel pump relay are melted and will cost $1500 to replace. Here is the picture they sent:
I've never dug into the fuel system and associated wiring on this car but have done it on my ML55's and I just can't imagine how this would cost $1500 to fix.
It doesn't help anything that they already ripped the harness out of the car. Seems like they are deliberately painting you into a corner to force you to pay for repair. They should have left the harness in the car and sent you photos of the damaged portions of the harness.
In every photo I've seen, the relay is melted and the insulation of the wires attached to the relay socket is burned off for about 1/2". You literally cut the socket off, crimp new connectors onto the wires, and reinsert into a new socket and use a new relay (while you are doing it, install a 70-amp relay rather than the stock 40-amp relay). If the fuel pump end of the harness is damaged (and they often are), purchase the new fuel pump adapter cable, cut off the damaged connector, then use one of the connectors off of the adapter cable. Decide if you are going to go with the revised pin out on the OEM harness or if you will repair the OEM harness and then install another adapter cable to match the parts catalog. It took me approximately 1.5 hours to replace the relay and socket and that included pulling and reinstalling the panels in the trunk. Add another 45 minutes to an hour for the harness under the rear seat.
If it were me, I'd tell them to replace the tank, push the car into the parking lot, and I would have it flat-bedded to my garage where I would repair it. FWIW, I literally did this once when I received what I thought was a BS diagnosis on another of my cars.
For more info, perform an Advanced search on "E55 fuel pump relay and fuse maintenance" using my user name. Read the entire thread.
It doesn't help anything that they already ripped the harness out of the car. Seems like they are deliberately painting you into a corner to force you to pay for repair. They should have left the harness in the car and sent you photos of the damaged portions of the harness.
In every photo I've seen, the relay is melted and the insulation of the wires attached to the relay socket is burned off for about 1/2". You literally cut the socket off, crimp new connectors onto the wires, and reinsert into a new socket and use a new relay (while you are doing it, install a 70-amp relay rather than the stock 40-amp relay). If the fuel pump end of the harness is damaged (and they often are), purchase the new fuel pump adapter cable, cut off the damaged connector, then use one of the connectors off of the adapter cable. Decide if you are going to go with the revised pin out on the OEM harness or if you will repair the OEM harness and then install another adapter cable to match the parts catalog. It took me approximately 1.5 hours to replace the relay and socket and that included pulling and reinstalling the panels in the trunk. Add another 45 minutes to an hour for the harness under the rear seat.
If it were me, I'd tell them to replace the tank, push the car into the parking lot, and I would have it flat-bedded to my garage where I would repair it. FWIW, I literally did this once when I received what I thought was a BS diagnosis on another of my cars.
For more info, perform an Advanced search on "E55 fuel pump relay and fuse maintenance" using my user name. Read the entire thread.
Best of luck to you.
Thanks for the response @bbirdwell ..........they ended up putting everything back together so I will be reading through your post and getting this done by myself. Thanks!
It doesn't help anything that they already ripped the harness out of the car. Seems like they are deliberately painting you into a corner to force you to pay for repair. They should have left the harness in the car and sent you photos of the damaged portions of the harness.
In every photo I've seen, the relay is melted and the insulation of the wires attached to the relay socket is burned off for about 1/2". You literally cut the socket off, crimp new connectors onto the wires, and reinsert into a new socket and use a new relay (while you are doing it, install a 70-amp relay rather than the stock 40-amp relay). If the fuel pump end of the harness is damaged (and they often are), purchase the new fuel pump adapter cable, cut off the damaged connector, then use one of the connectors off of the adapter cable. Decide if you are going to go with the revised pin out on the OEM harness or if you will repair the OEM harness and then install another adapter cable to match the parts catalog. It took me approximately 1.5 hours to replace the relay and socket and that included pulling and reinstalling the panels in the trunk. Add another 45 minutes to an hour for the harness under the rear seat.
If it were me, I'd tell them to replace the tank, push the car into the parking lot, and I would have it flat-bedded to my garage where I would repair it. FWIW, I literally did this once when I received what I thought was a BS diagnosis on another of my cars.
For more info, perform an Advanced search on "E55 fuel pump relay and fuse maintenance" using my user name. Read the entire thread.
@kenbenz803
PM me your email address and/or cell phone number. I'll see what I can do. It's not rocket science and 2-3 hours of your time all can be good.
Hey guys, my 05 E55 is at the dealership for the fuel tank, fuel pump, etc extended warranty. As I should have expected, there's always more to the story once the car is in shop being worked on. I get a call that the fuel pump wiring harness and fuel pump relay are melted and will cost $1500 to replace. Here is the picture they sent:
I've never dug into the fuel system and associated wiring on this car but have done it on my ML55's and I just can't imagine how this would cost $1500 to fix.
Thoughts here?
Thanks!
That's absurd! Even with MB's sky-high parts costs, that's WAY over the top. Reading through bbirdwell's reply below, he describes a process of splice-to-repair with an estimated time of 1-2 hours to do the work. Replacing the full harness plug to plug (assuming it's the same as the one shown in your photo) should take about 1/2 that amount of time...
Last edited by CapeFearElvis; Jan 19, 2026 at 06:49 AM.
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