Troubleshooting windshield washer pump issue, completely stuck!

[AirPuffedSugar]

Hello! First post on the forum, let me know if I'm doing something wrong!! 

 

I've got an 01 Silverado 1500 4.8L, 4x4, ext cab.

 

When I bought the truck it the windshield washer pump worked, but the next time I went to use it, it coughed fluid once and that was it. When engaging the washer pump switch, the pump cannot be heard so there's no chance of a plugged line. No fluid leaks, and yes the reservoir is full! As well, I'm aware that the washer pump is engaged by the tab on the combination switch, it seems to be a common mistake people have made. 

 

First thing I did was check the W/W PUMP fuse under the hood, it's fine. Even swapped it for a couple other 15A fuses just in case. All of my windshield wiper functions work perfectly barring the washer pump, so a combination switch issue seems unlikely. I replaced the washer pump itself, nothing. With the key turned to ignition, I tested for power at the washer pump plug with a multimeter (measuring DC volts), nothing. No power at the fuse slots either. Thinking the combination switch may be at fault anyways, I switched it out for one at a pick'n'pull. Still no dice, and all other functions work perfectly. 

 

This diagnosis tells me that the issue doesn't lie within the combo switch, pump, or fuse. My best guess is one of two potential things. It might be a bad ground, which should be easy enough to fix. Or, I'm thinking it's potentially a bad wire running from the fuse box over to the combination switch, but I'm hoping I won't have to pull apart that huge bundle of wires and messing with the seal on the firewall! If this is the route I have to go, what's a good way to go about it? 

 

I've included the wiring diagram for the entire windshield wiper system of my vehicle below for reference. The far left side is pretty much everything I need to worry about at the moment if I'm reading it correctly (I'm brand new to wiring diagrams, electrical circuits, and multimeter diagnosis so I apologize if I'm missing something super obivous!)

[trk98]

i'm no wiring expert, but that diagram almost looks like the washer pump fuse is only hot when the switch is engaged. Maybe try testing for power while the switch is activated.

I believe the wiper fuse should be hot when the key is in the "on" position.

Hope I didn't steer you in the wrong direction. Good luck!

[AirPuffedSugar]

Sorry, I should have added that! Yes, I'm engaging the switch when checking for voltage in any location!

[rjgti]

check for power at e4 and e9. for e9 check you will need washer switch engaged

[sefiroxx]

Check the 25a washer fuse. It aupplies power to the while system. The switch then provides power thru the pump fuse to the pump. The pump fuse is an additional fuse that is used to protect the control from a short I the wet pump environment.