 Fuel pump polarity (&other questions) |
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| jmitro |
 Dec 22 2017, 07:10 PM
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#1
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Senior Member  Group: Members Posts: 713 Joined: 23-July 15 From: Oklahoma Member No.: 18,986 Region Association: None 
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I’ve searched for 3 hours and cannot find the polarity of this Bosch in-line fuel pump. The terminals are not labeled positive or negative, only a smaller M4 terminal and larger M5. Which one is positive and which is negative?
For chassis wiring - the (EDIT) brown is ground and black/red is positive, correct? finally, if I locate the pump to the trunk, how do I back track the wiring from the engine compartment to the trunk? it still needs to go through the relay which is in the engine bay Attached thumbnail(s) 
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| JeffBowlsby |
Dec 22 2017, 07:47 PM
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#2
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914 Wiring Harnesses Group: Members Posts: 8,533 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None
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I dunno. But if the case is grounded there may be continuity between one of the terminals and the case. Maybe?
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| 914Sixer |
Dec 22 2017, 10:10 PM
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#3
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914 Guru Group: Members Posts: 8,903 Joined: 17-January 05 From: San Angelo Texas Member No.: 3,457 Region Association: Southwest Region
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I will look at a pump I have tomorrow. I am thinking the larger is ground and smaller is positive.
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| MarkV |
Dec 22 2017, 10:33 PM
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#4
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Fear the Jack Stands Group: Members Posts: 1,493 Joined: 15-January 03 From: Sunny Tucson, AZ Member No.: 154 Region Association: None |
Big one is positive....small one is negative.
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| jmitro |
Dec 23 2017, 05:29 AM
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#5
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Senior Member Group: Members Posts: 713 Joined: 23-July 15 From: Oklahoma Member No.: 18,986 Region Association: None
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that's what I thought also, but in searching other forums I saw the opposite.
The instructions with this pump had nothing about polarity and do not even show the direction of fuel flow. (IMG:style_emoticons/default/headbang.gif) I finally figured out the outlet was the smaller port next to the terminals |
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| TheCabinetmaker |
Dec 23 2017, 08:10 AM
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#6
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I drive my car everyday Group: Members Posts: 8,304 Joined: 8-May 03 From: Tulsa, Ok. Member No.: 666 |
there should be a small +&- on the towers below the threaded connections
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| Front yard mechanic |
Dec 23 2017, 08:36 AM
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#7
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Senior Member Group: Members Posts: 1,172 Joined: 23-July 15 From: New Mexico Member No.: 18,984 Region Association: None
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Simple hook up power and test pump it with water I've done this many times and the water doesn't ruin the pump. Then run it dry for a few to drain the water
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| jmitro |
Dec 23 2017, 10:36 AM
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#8
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Senior Member Group: Members Posts: 713 Joined: 23-July 15 From: Oklahoma Member No.: 18,986 Region Association: None
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QUOTE(The Cabinetmaker @ Dec 23 2017, 08:10 AM)  there should be a small +&- on the towers below the threaded connections ah, yes you are correct. the marks are tiny, but they are there. my 45 year old eyes just missed it. It's notable the SMALLER M4 terminal is positive, and larger M5 is ground thanks all (IMG:style_emoticons/default/beerchug.gif) |
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