77 530i top of gas tank wires?

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canada karl
Posts: 1058
Joined: Tue Jan 06, 2009 3:50 pm

77 530i top of gas tank wires?

Post by canada karl »

There is a round plate on the top of the tank that has a 3 wire connection. The wiring colors are faded out. I'm guessing that one is power and one is ground but can't figure out the third wire. The connection and wire ends were totally rusted out so I replaced the wiring. The wiring diagram dosn't appear to show this connector?
1976 530i. BMW 59 Triumph TR3A(rolling resto). 67 Triumph TR4A(salvageable). 86 900S Winter car
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Robert Bondi
Posts: 338
Joined: Sun Jan 11, 2009 12:33 am
Location: Austin, TX

Re: 77 530i top of gas tank wires?

Post by Robert Bondi »

No pre pump on the 77, so that must be your fuel level sensor. Three wires makes sense since it's basically
a potentiometer. One connection on each end of the resistor and the third connection provides partial resistance as the float moves across the entire resistor.
Robert
77 530i
77 Euro 528
canada karl
Posts: 1058
Joined: Tue Jan 06, 2009 3:50 pm

Re: 77 530i top of gas tank wires?

Post by canada karl »

Thanks Robert I see what you mean. I replaced the left and right connectors with new wires The 3rd connector had rusted off so I left it Now the fuel gauge reads almost full when there is less than half a tank there. The 77 was the year they switched to the Pass side gas tank filler. They also switched the way the sending unit assembly cap with the connectors was held down. In my 77 car (side filler) the plate with the connectors is held down by bolts that are now severely rusted. I would like to replace that plate with the good one from the 76 but that tank cap does not have hold down bolts.....maybe a spin on cap??? I'm reluctant to make the swap because of the different ways that the two caps are held down.

I just looked in my box of parts that came with the 77 and found a sending unit assembly with the bolt hole plate. How do I test this unit to see if it works? Also is the round black plastic connector on the sending unit removable???
Cheers
Karl
1976 530i. BMW 59 Triumph TR3A(rolling resto). 67 Triumph TR4A(salvageable). 86 900S Winter car
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