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Posted by: jmitro Dec 22 2017, 07:10 PM

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


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Posted by: Jeff Bowlsby Dec 22 2017, 07:47 PM

I dunno. But if the case is grounded there may be continuity between one of the terminals and the case. Maybe?

Posted by: 914Sixer Dec 22 2017, 10:10 PM

I will look at a pump I have tomorrow. I am thinking the larger is ground and smaller is positive.

Posted by: MarkV Dec 22 2017, 10:33 PM

Big one is positive....small one is negative.

Posted by: jmitro Dec 23 2017, 05:29 AM

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. I finally figured out the outlet was the smaller port next to the terminals

Posted by: The Cabinetmaker Dec 23 2017, 08:10 AM

there should be a small +&- on the towers below the threaded connections

Posted by: Front yard mechanic Dec 23 2017, 08:36 AM

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

Posted by: jmitro Dec 23 2017, 10:36 AM

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