Question About Fuel Pump 1980 450SL

[Lawrence Coppar]

The fuel pump relay on my 450SL is acting up. I ordered one but the replacement (used one) will not run fuel pump when key is turned to on (not start). The 25 year old original one always ran the fuel pump for a few seconds to pressurize the system prior to starting. It would shut off after pressurization was completed, then restart when engine is turned over by starter. New relay will not start car nor does it send any voltage to the pump at any time. I have a multimeter attached to pump terminals to eliminate a faulty fuel pump so I know it is not receiving any voltage.

The original relay will not run the pump once the car has been run for a while until I let the car sit for some time. That is why I ordered another relay.

The person who sent me the relay said it is the correct one. He knows a lot about the cars. Any ideas what is going on here?

[230/8]

The relay should have a small functional diagram engraved into the metal cover, the amperage rating listed, and also it will have each terminal designated by number to match the diagram. First compare the diagram on the replacement with the orignal, they should match. If the amperage rating is the same then you probably have a defective replacement. Check this site for a new replacement, it should be less than $30. Buy a spare for your glove box because it is a common style.

230/8

[boomer]

Recently bought '80 450SL. Ran great 150+ miles home. Sat for 2 weeks till I could start working on it,needs lt rr qtr, and battery was dead. Recharged batt and car ran fine. Left idling while I opened shop doors and it died and will not start. No power to Fuel pump. Where are relays located? My first Benz , but I've always wanted a 450.

[Lawrence Coppar]

Relays are located above fuze box on passenger side. I remove the long metal piece that parallels the door, then the short metal (vertical) piece in door jam. Then remove the part that surrounds the fuze box. One screw and a lot of jiggling removes it.

Fuel pump relay is lower right. It is the large black plastic covered one just to right of small silver colored one. It's in a bad location and difficult to get in and out.

[Lawrence Coppar]

Originally Posted by 230/8

The relay should have a small functional diagram engraved into the metal cover, the amperage rating listed, and also it will have each terminal designated by number to match the diagram. First compare the diagram on the replacement with the orignal, they should match. If the amperage rating is the same then you probably have a defective replacement. Check this site for a new replacement, it should be less than $30. Buy a spare for your glove box because it is a common style.

230/8

The relay costs over $100.00. Wish you were correct.

[230/8]

Lawrence:

If your source is quoting you $100, with all due respect, you may need a new source. I just bought one from my local indy for $30 retail.

230/8

[Lawrence Coppar]

The parts quote on this website is 117 bucks. What does local indy mean?

[230/8]

Looks like your '80 uses a six-pin relay. Mine uses the more conventional and cheaper five-pin relay which are quoted at $23.50. Looks like they switched around '76; probably related to something in the emission control. Too bad for your wallet.

An indy is an independent mechanic. I have a trusted fellow who works on mine sometimes. He prefers the older cars and always carries a good stock of all the right stuff which I frequently tap into rather than mail ordering.

230/8