Hi Guys,

I'm actually a 2002 SLK 320 (R170) owner but I believe that the SLK and Crossfire are close relatives from what I've discussed whilst trying to resolve this issue.
I hope that's correct and you guys don't mind me seeking assistance here.

Anyhow, only had the SLK a few weeks and the blue 15amp fuse in the F5 slot of the K40 relay (Relay Control Module) kept blowing.
(On UK models the K40 module sits under the bonnet (hood) on the drivers side right next to the battery.

I noticed some electrical tape in this area so I undid it to find this mess.

http://s18.postimg.org/jrkyssjrd/01_Wiring_Mess.jpg

The red wire (yellow arrows) had been cut in half and one end taped up and left dangling, the other end crudely joined to the pink/green wire (orange arrows)

I undid this mess and returned it to its original set up the best I could.

Hey presto the fuse has stopped blowing however now the fuel pump will not turn off.
At least I think its the fuel pump, its a humming from behind the rear wing where the fuel cap sits (drivers side).
Its constant, I have to disconnect a wire or the battery if the car is left for a few hours otherwise it drains the battery.

What would the reason be to rewire the area shown in the image?

They've also knackered the plug on the end of the dodgy wiring that connects to the K40.

http://s18.postimg.org/5jva4572h/02_Plugs_Mess.jpg
http://s18.postimg.org/dbc02pb7t/03_Busted_Plug.jpg

Other than the fuel pump issue the car now runs fantastically, I do a 35 mile round trip commute every day. Is it likely the fuel pump is knackered even though the car runs great, could it be the K40 or the relays inside it even though it looks like new, the solder seems great, there are no charred areas at all or cracks, I've done a lot of reading on this K40 module I feel like I know it well, or is it likely to be the wiring itself between the fuel pump and the engine bay?

I'm happy to send it to the garage but I want to try and learn things before I pass it on and I have little faith in the diagnostic skills of 'some' garages if I'm honest, been burnt before.

I'm trying to locate a replacement for the busted plug but no internet search is showing anything resembling that plug, anyone know what it's actualy name or part number is?

Any suggestions would be most welcomed, I hope the images load ok and this is enough info for you guys.

Thanks in advance, Bren

 

If you weren't so bleedin' far off-I'd offer to help track the POS down and kneecap him for doing this.

'Effing amateurs...
I'm not offering any help here-just hand-holding, sir.

Except this-find an SLK or Crossfire in a breaker's yard and buy the connector. Splice it back in using solder and heatshrink tubing. A good start, anyways...

 

If the wiring is REALLY back to normal and the pump wont' turn off, that would mean that the fuel pump relay is stuck closed - replace the fuel pump relay.

Now, this ASSUMES that the car is set up like the Crossfire, the hot side of the fuel pump relay's contacts goes to splice block 100 which is hot all the time.
So you see, if that relay is stuck or welded in the energized position, then yes, the pump will run all the time.

My guess is some asshat tried finding a different source of switched A+ (12 volts) because he didn't want to change the relay or did not understand what a relay is.

 

Plus 1 on pizzaguy. If I were you I would also try to find the service manual for the schematics including the wiring color codes, to help find out where that extra wire goes to, and to try to find out what the other guy(s) did to the wiring. Once you get it back to what it should be, you can maybe find someone with a 'K40' module to see if it then works correctly. Good luck!


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Or pop the cover off the K40 and have a look at the fuel pump contacts :

 

Exactly like pizzaguy alluded to/said in his first sentence. Great picture George!


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I claim no credit, that's onehundred80's picture.

 

SOLVED: Fuel Pump Permanently On
My apologies for the delayed response to all the very useful messages and information that you guys posted. I feel at home here already and I really appreciate it. I've had some drama's so wasn't in the state of mind for internet stuff, back on track now :-).
After speaking to 2 garages and one friend who is an eletrcial engineer and a great source of auto knowledge and coming up with no definitive answer I decided to take the plunge and simply replace the K40 relay or whatever name you wish to use for it, seems to differ :-) This seemed to be the recommended course of action.
The fuel pump issue was instantly resolved, it now turns off as soon as the car is turned off, even left it stood over the weekend as I was on the beer and on Monday it fired up no problem so doesn't appear to be any drain at all on battery.
K40 has only been replaced a week now but the intermittent cutting out and and more intermittent failing to start (not even turn over) also seems to have stopped, I will post updates regarding this issue over the next few weeks as only driving it will let me know for sure.
Strangely, or not if you know more about cars than I do, the car is running beautifully, far smoother and responsive than prior to the K40 module being replaced. It is NOT my imagination lol.
I purchased the part online and the guy even through in all the plugs and wires so I cold replace the one that someone had butchered, so far a great result all round.
Interestingly, one of the plugs he sent me that I did NOT need has 2 wires coming from it while my original, and as far as I thought, untouched plug, only has one wire so I now have a spare wire coming from the central black plug on the K40. Everything works on the car as far as I can see so what is it for?
Any idea to what the stray wire should connect to? I'll try post an image or make one available.
If this works its the wire on the right, its red and green.

http://s22.postimg.org/fzpsvlzcx/IMG_0287.jpg

Any feed back would really be appreciated and certainly put my mind at rest, maybe :-)

Thanks in advance

Bren

 

Here ya go, the pinouts for the K40 / RCM :

 

My only guess is the relay was sticking on, and whatever corrosion/bridging on the contacts was causing a resistance, and not supplying full power to the fuel pump. Other than that, no idea.

 

Thank you Xfire it seems the wire is the "Fused Traction System Relay Output" (Red/Green), this should help me trace it back to where it should connect, the diagrams are spot on, much appreciated.

Pioneer: Yes I checked all aspects of the K40 as thoroughly as I could, I even used the microscope at work, I couldn't locate any of the often cited issues such as bad solder, charring, and the relay when exposed did 'seem' to switch between on/off when the car was started and functions were operated, I confess my knowledge is limited I'm trying to educate myself through certain literature and of this site which quite frankly is bloody amazing. Seems to be a great community on here so far.

Thank you.