Chevrolet Repair: Passenger sending unit, fuel inj, gmc sierra

Question
QUESTION: Does my 1979 gmc sierra grande passenger tank have 2 or 3 line sending unit. its gas and has a 20 gallon tank.

ANSWER: HI KEVIN, I WILL NEED TO LOOK THIS ONE UP AT MY WORK FRI MORNING. WHAT ARE YOU DOING AND WHY DO YOU NEED TO KNOW THIS JUST SO I UNDERSTAND WHAT IS GOING ON ??? NOT BEING NOISEY..BECAUSE IT HAS 2 TANKS IT MAY HAVE 3 LINES. MAIN,VAPOR RETURN AND CROSSOVER TO THE OTHER TANK..JUST A HYPOTHESIS..GET BACK TO ME AND I WILL LET YOU KNOW FRI AM..TOM

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QUESTION: I changed fuel pump and it wouldn't start so after sitting for a few weeks I tried it  again and oot started. Well I have a little hole in my passenger tank so I'm buying. new one cause its rusted inside. There's no driver side tank on  
That's how I bought it. So not sure if I need 2 or 3 line sending unit

Answer
HI KEVIN,,WELL IF YOU ONLY HAVE ONE TANK JUST GET A SENDING UNIT FOR 1 TANK ONLY. THIS HAS A CARBURETOR SO FUEL INJ DOES NOT COME INTO PLAY. USUALLY A SINGLE TANK HAS 1 LINE TO IT UNLESS THIS YEAR HAS A VAPOR RETURN LINE...WHICH WOULD BE EASY TO CK. JUST LOOK AT THE LINES GOING UP TO THE FUEL PUMP..IF 2 LINES TO THE LOWER SECTION OF PUMP THEN YOU HAVE A VAPOR RETURN LINE AS WELL AS THE MAIN FEED LINE WHICH WILL BE 3/8 " AT THIS POINT I WOULD GET THE CHEAPEST SENDING UNIT YOU CAN GET WHICH WILL BE THE SINGLE LINE OR 2 LINE. I WOULD ALSO RUN NEW COPPER LINES UP TO THE FUEL PUMP TO MAKE SURE THEY ARE CLEAN..LET ME KNOW HOW THIS WORKS OUT FOR YOU..IF YOU NEED MORE INFO GET BACK TO ME..TOM..