Hello everyone, first post, so go easy please.

I have a (US spec, in case that matters) 2004 r50 with a windshield washer problem. When I bought the car, the rear window sprayer would work, but the windshield sprayers didn't.
I pulled the pump off the reservoir thinking it was either bad or clogged, and hooked it up to a water supply and a 12 volt power supply. The pump sent fluid out one output with the polarity one way, and reversing the polarity sent fluid out the other output. So it seems the pump seems works. Also, connecting the pump to the water lines on the vehicle, both front and rear sprayers test out just fine - not clogged.
Putting a voltmeter on the vehicle wiring harness plug, I get +12VDC when the rear sprayer switch in the car was activated, and -12VDC when the front sprayer switch is activated (flipping the voltmeter leads reversed whether the voltmeter reads + or - 12VDC, depending on which switch in the car is activated).
However, plugging the pump directly into the vehicle wiring harness, only the rear sprayer works. Also, I used a set of jumper wires from the vehicle wiring harness to the voltmeter and to the pump, just to see if the wiring harness maybe wasn't making a good connection with the pump, but I still get the same results - pump works the rear sprayer, but not the front.
I do have a replacement pump I purchased and am getting the same results with the replacement pump.

From what I understand, the electrics (switch, fuse, wiring harness, pump connector) work if I'm seeing both + and - 12VDC when the vehicle sprayer switches are activated, and the pump(s) are working as they should if they are pumping water out one or the other outputs based on applying +/-12VDC from the external power supply.
I've also tested the fuse and the relays in the washer system; everything tests just fine.

I'm at a loss as to why the pump will only operate the rear window output when plugged directly into the vehicle???

What am I missing?
Thanks all,

Raxx