Fuel Pump Only working when "hot wired"

[BMW BWW]

My 1988 325i recently stalled while in a parking lot.
It would turnover, but would not start.
My initial assessment was fuel, and after performing all of the standard tests, all signs pointed to the fuel pump.

I Replaced all Fuses and Tested Relays - everything was operational and checked out.

Upon removal of the rear seat, it was revealed that, indeed, the fuel pump was not operating.
I removed the pump, and decided, on a whim, to give it juice via my battery charger. It ran flawlessly. I assumed, at that point, (because all of my tests pointed to the FP), that this was merely the result of the pump receiving extra, and possibly more steady than normal, voltage.

I purchased a new pump, but, prior to installation decided to check several things.

First, I checked the voltage 'to' the pump, at the connection, under the seat. I was at, our near, battery voltage. I also checked the voltage from my charger to the old pump and discovered it was identical to that being sent to the pump in the car. This was cause for concern. Without inserting the new pump into the tank, I briefly connected it, and discovered that it too was not running under power from the car, but would, off of the charger. I re-installed the old pump, and, via 'jumping' the fuel pump could get my car to start and run smoothly. When I reconnected it to the car/power source, the car lost fuel pressure and stalled shortly after.

I am completely puzzled as to how relays and fuses could all be operational, voltage at the pump could be identical to an 'outside' power source, and yet the pump fails to operate when being powered by the car itself. (I will add, that because this is a convertible, the battery is in the engine compartment, thus the normal fuseable link answer does not necessarily apply - and - I have voltage at the pump!)

Is it possible to have voltage, and yet have something else triggering the operation of the pump? Is there something I'm overlooking? Please advise.

Brad

[FLG]

Check the fuel pump relay under the hood on the driver fender, it should have a black cover over it. Sometimes they pop out or simply go bad.

[jlevie]

Check the pump ground.

[BMW BWW]

jlevie - Last night I began wondering if that could potentially create this scenario. That being said - where / how would I check this? Thanks!

FLG - all relays were checked prior to posting, and are operational. Thank you, though.

[BMW BWW]

After checking all connections and cleaning all easily accessed contacts, nothing changed. I was able to connect the ground/brown/negative side to the pump, and run wire to the battery and have it operational. I then chose to run a new positive wire, from just under the fuel relay. (This would be the green and purple wire.) Everything is now perfectly operational. At the end of all of it, it cost me 6 bucks and a bunch of time. My assumption is that I either have a short, corrosion, or simply old enough wiring that power was reaching the fuel pump, but not consistently strong enough to fire.