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

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

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

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

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

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

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

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