Fuel Sending Unit: Which wire is positive?

[artguy]

'94 530i: Getting ready to install a new fuel pump and fuel sending unit...as soon as it stops raining & snowing outside

Question: The fuel sending unit has two wires that attach to the pump. One is purple and one is brown. How do you tell which is the positive and which is the negative?

Those wires have the older "ring terminal" connectors for the older style pumps. The new pumps require you to cut those wires and attach plug sleeves which then slide onto posts on the pump. The pump indicates which post is positive and negative...but I'm not sure which wire to attach where?

Anyone dealt with this recently?

FOLLOW UP: Brown is Ground and Purple is Positive

[bmwrp8]

not really sure but hope this helps.
http://bmwe34.net/e34main/maintenanc...MW%20525iT.pdf

[Dave M]

My rendering of the sending unit side of the connector (I re-wired it due to corrosion).



On mine, the "brown ?" at top left is (-), the "Large gr/vi" at top right is (+). You state you have a purple, so its either the same green/violet on mine or a different color. Just find the colors at these locations and they 'should' be the same when they emerge at the pump.

Hope it helps,

Dave M

[timandbim]

...i think.... haven't seen a brown wire yet that isn't neg or ground either in diagrams or in my car. good rule of thumb maybe, unless you're playing with gasoline... then maybe you should be extra sure

[whiskychaser]

...i think.... haven't seen a brown wire yet that isn't neg or ground either in diagrams or in my car. good rule of thumb maybe, unless you're playing with gasoline... then maybe you should be extra sure

You wont get a job as an electrician in the UK - brown is industry standard for live

[artguy]

You wont get a job as an electrician in the UK - brown is industry standard for live

So it's manufactured in the Czech Republic...do you think they follow the UK standard as well?

[timandbim]

You wont get a job as an electrician in the UK - brown is industry standard for live

heh- dude, i wouldn't get a job at a tea shop in the UK!

but i'd like to know.... 'cause every brown wire i've seen on my car is either a common ground or a neg. i always double check with a schematics page, but that seems to be the case on my '89 at least.

[whiskychaser]

So it's manufactured in the Czech Republic...do you think they follow the UK standard as well?

What I think is that brown isnt always ground

[Claude]

not really sure but hope this helps.
http://bmwe34.net/e34main/maintenanc...MW%20525iT.pdf

Question ? According to diagram on this file the fuel sander is fasten to the fuel tank but the fuel pump seems to be put completly loose in the bottom of the fuel tank, just connected to the sander plate by hoses (The Bentley does not show much more detail about that); is it really the case ? I must have miss something, could you explain plse.

[artguy]

According to diagram...could you explain plse.

As good as the Bentley is, it does lack things at times.

The fuel pump is attached to the fuel sending unit by two wires and two hoses. Here they are together:


In the tank the fuel pump sits in a cradle which is attached to the inside of the tank. Here is the cradle on the bottom of the tank:


And here is a picture of the pump installed in the cradle while still attached to the sending unit (Note the pump release tabs):


I just got these parts out last night. So now I will be able to tell which wire is positive and which is negative and post the solution to this original post soon.