1986 Audi 5000 Fuel Pump Relay Operation

1986 AUDI 5000
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JOHNGOTTS
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1986 Audi 5000S Front Wheel Drive Automatic 92450 miles

Although I understand how a simple relay circuit works for a fuel pump, I need an explanation of the control for the relay in this car which uses a Hall-effect transducer and an ignition control unit. I don't understand what it takes to energize the relay. The one I have is unreliable and will work most times. Then again, I can get in the car and the relay won't energize. The relay was replaced. This is the circuit.
References as follows:

Input 30-Batt 12V
Input 15-12V Switched from ignition
Input 31-Gnd
Input d-ignition coil term. 1 fed from ICU outputInput e-02 sensor heater
[img:8b590bd71e]http://www.2carpros.com/forum/automotive_pictures/531412_fuelpump_1.jpg[/img:8b590bd71e]
May 25, 2010 at 4:41 PM
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MERLIN2021
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This is a tech tip from Audi to the dealers... look at this.
DEAD AUDI FUEL PUMP - INSULATE/CLEAN CONNECTION TECHNICAL INFORMATION TIP Reference Number(s): AUD0421AP,  Date of Issue:   December 1989 Related Ref Number(s): AUD0421AP ARTICLE BEGINNING VEHICLE QUITS RUNNING WHEN FUEL PUMP LOSES POWER YEAR(S): 1978-88 MANUFACTURER: Audi MODELS: 4000; 5000 DATE OF ISSUE: December 1989 ISSUE & TIP A number of Audi 4000 and 5000 models have quit running when the fuel pump lost power. The green and yellow power supply wire to the fuel pump goes through a connector beneath the rear seat. We remove the rear seat cushion to solder and insulate the connection. (Editor's Note: We have also gotten some reports that the ground connection for the pump, which is also located beneath the rear seat, can corrode, causing a similar problem. This is ground connection number 14 in the Audi wiring diagram. You might as well clean and tighten this connection while the seat is removed.) Courtesy of Import Service Magazine with thanks to: Frank Hanrahan Haus of Performance Costa Mesa, California REFERENCE NUMBER AUD0421AP NOTE: This information has been obtained from sources generally believed to be reliable. Use your own judgment before relying on this data.
May 28, 2010 at 12:39 PM
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RDEAN123
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Oh so that's how it works? I know I know you guys can call me a noob when it comes to these things but at least I'm trying to learn. Been browsing this forum for hours already and I've learned a lot for my Audi. Thanks guys.
May 31, 2010 at 10:21 PM
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