We tried putting more fuel in the tank, and someone told us to put fuel in the carb, it started the car, but as soon as the fuel in the carb ran out it died again. Is the fuel pump located in the tank? Does anyone think that it might be something else?

The pump is located in front of the rear passenger wheel.

You either have a bad pump or a bad relay. Test the pump by bridging the pins on the relay socket or by applying 12v directly to the pump.

If the pump is good you probably have a bad relay. Try smelling it. It should have a burned odor.

Remove the fuel pump cutoff relay and jump two of the pins: 87 and 15. If it starts, your relay is bad. If your relay is bad, your fuel pumps probably shorted it. May as well replace the relay and the pumps, or you'll keep burning through $150 relays.

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2003 S500 Black/Charcoal
1990 560SEL 61k Arctic White/Grey

SOLD:
1988 420SEL Black/Palomino Sold @ 85k
1987 420SEL Midnight Blue/Grey
1986 420SEL Diamond Blue/Grey
1983 380SEL Champagne/Palomino

how do you jump the pins?

Jumping the pins means creating a direct electrical connection between the two pins in question (i.e., with a piece of insulated wire with appropriate connectors crimped or soldered on each end). The trick is to ensure you don't accidentally create an electrical connection with a third pin while doing so (potentially $$$).

What carb?? A 420 sel has fi for all years, right?

I went to James Motors in Lexington Kentucky and purchased a relay and changed the pump. Worked like a charm. It started right up and is running fine except for a lot of white smoke now. I suppose that is just from sitting, but I am going to change the oil and get a tune up tomm to see if that helps.