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  #1  
Old 06-23-2015, 04:03 PM
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No 12v to fuel pump

My 1972 350sl won't start. I check to wires to fuel pump, not hot. If I run a set of jumpers back to the fuel pump it will start, and the wires that I disconnected are now hot. There is something stopping the motor from starting and allowing the fuel pump to start pumping. In a perfect world the car will start and 2 or 3 seconds later the fuel pump gets 12v to keep it running. Any help would be great.
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Old 06-23-2015, 05:28 PM
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Originally Posted by sallyles4645 View Post
My 1972 350sl won't start. I check to wires to fuel pump, not hot. If I run a set of jumpers back to the fuel pump it will start, and the wires that I disconnected are now hot. There is something stopping the motor from starting and allowing the fuel pump to start pumping. In a perfect world the car will start and 2 or 3 seconds later the fuel pump gets 12v to keep it running. Any help would be great.
First of all, you only get 12V to your pump for a second or two after you turn key on. To check if you have power to pump, you would have to jumper the fuel pump relay. Or connect meter to pump and have someone turn ignition key on while you watch the meter. It should just show 12V briefly.

If after testing you still don't have power to pump, then ...

There are two items that control power to fuel pump.

A fuel pump fuse.

A fuel pump relay.

Fuse is just one of those in fuse box. 8amp, I believe. Forget which one.

Relay is one in pic below (located above fuse box) You can switch it with one of the others (they are all the same) and see if you then get power to your pump.

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85 300D14 GLK250,72 350SL, 98 E320
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Old 06-24-2015, 02:11 AM
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Thanks Graham, I will test it tomorrow, I have a spare relay if that turns out to be the problem. The fuse panel has no listing for fuel pump, but I will test them all.


Thanks
Les
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Old 06-24-2015, 10:58 AM
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Originally Posted by sallyles4645 View Post
Thanks Graham, I will test it tomorrow, I have a spare relay if that turns out to be the problem. The fuse panel has no listing for fuel pump, but I will test them all.


Thanks
Les
They kept changing the fuse layout, but according to the 350SL wiring diagram, fuse 14 feeds both the main EFI relay and the fuel pump relay.
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85 300D14 GLK250,72 350SL, 98 E320
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Old 06-27-2015, 07:49 PM
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I had that problem and found water under my backseat carpeting had corroded the plug
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Old 06-29-2015, 02:47 PM
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some old cars you need to run a new circut.I have tapped into fuse panel on older cars to run fuel pumps,injection line heaters.It would be could if you could find a switch that would shut off pump in a wreck,with a reset switch
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