[JHanson907]

Our 1988 560 SEL, VIN WDBCA39D8JA379776, has had recent problems w/ intermittent no-start and/or dying on the road issues. We would wait a few minutes and it would usually start right up okay. Recently we have had more serious problems and have had to have it towed home (embarrassing, I know!). At first I thought it was an intermittent fuel pump problem and/or fuel filter issue. Deeper troubleshooting indicated we have a problem, at least indicated, at the fuel pump relay (see photos). Pin #30 on the relay (#8 on the receptacle) has been getting very hot and has started to melt the plastic around the pin receptacle.
Questions:
1. What could cause this problem of overheating pin?
2. Where can I buy a replacement "receptacle" for the fuel pump relay?
3. Is there a procedure to test the fuel pump relay to determine if it is damaged internally (my MB shop manuals do not indicate any test procedure)?
4. Where can I buy a replacement fuel pump relay?
Thanks!

 

[John350]

Pin 30 is where the power comes into the relay to feed the pumps. When it burns like that it's usually caused by corrosion or a loose socket, or both. This causes resistance and resistance generates heat. The heat in turn causes the connection to loosen up and it's a vicious cycle from there.

Clean up the pin and the socket. Make sure it's a tight fit on the relay and make sure it gets plugged all the way in. Put some dielectric grease on the pins. Clean, tight, and lots of surface area and it'll work fine.