[AzTaco]

Greetings. Been reading a lot since I got my 2000 Excursion 2WD 7.3L last year to tow some toys. Lots of little things I need to fix and this site has been a great source.
About 3 weeks ago my vents defaulted to the defrost position. I assumed the pump died. I disconnected the vacuum pump connector and using a borrowed Power Probe I was able to power the pump (neg alligator clip on neg, probe on pos, push button). I probed the connector with my multimeter (KOEO) and I only get 3.2V. I started the engine and I get up to 3.5V as I throttle the gas but no higher. I put my neg multimeter probe on the neg connector contact and touched every ground I could see and got a beep (didn't measure values). So I assume my grounds are at least there. All passed the wiggle test too.
Trying to take the GEM out of the loop I took the fuse box and GEM out. No corrosion or signs of water intrusion. I found another fuse box/GEM at a salvage yard for $20 and swapped that in hoping it would address not only the vacuum but a few other things. No change, vacuum still not working and it's only 3.2V at the connector.
Any ideas on where to search now? Luckily it's getting cooler here in the desert so I can open my windows, but this is annoying.

 

[klhansen]

The vacuum pump is powered by Fuse 28 in the central junction box (under the dash) that is hot with key on.
So if you aren't seeing 12V on the pump connector, then look at the circuit powering it. It could be a high resistance connection somewhere. It could also be a problem with the ignition switch in the circuit that powers fuse 28. The vacuum pump has a built-in switch that shuts it of when it develops enough vacuum.

The GEM is not involved with the vacuum pump. If you swapped in a GEM, it would need to be programmed to work with your Excursion. I would put the original back in to avoid having to program it.

 

[AzTaco]

The vacuum pump is powered by Fuse 28 in the central junction box (under the dash) that is hot with key on.
So if you aren't seeing 12V on the pump connector, then look at the circuit powering it. It could be a high resistance connection somewhere. It could also be a problem with the ignition switch in the circuit that powers fuse 28. The vacuum pump has a built-in switch that shuts it of when it develops enough vacuum.

The GEM is not involved with the vacuum pump. If you swapped in a GEM, it would need to be programmed to work with your Excursion. I would put the original back in to avoid having to program it.

Thanks. The ignition switch is going to be the next thing I replace. Easy to get to and cheap so not worth much multimeter investigation. There's several taps to the wiring going to the ignition switch so it could be there's an issue there with something coming loose as well. Wish that was an easy pigtail to replace.

By chance, do you know what the 2 large gauge twisted black wires are? They go up into the steering column and are fairly long. Mine are just dangling but being tightly twisted together something tells me they are a bit more important than just some small gauge wire. I couldn't find them on the wiring diagram, but could have easily missed them.

I picked up the fuse box/GEM from a same year/trim Excursion so it should be ok. My truck is also the victim of an engine swap (5.4L gas to 7.3L diesel - long story) and the fuse box/GEM was for a 2001 4x4 SUV/truck based on the GEM sticker. So if anything what's in there now is closer to correct than what was there

Thanks for replying.

 

[klhansen]

By chance, do you know what the 2 large gauge twisted black wires are? They go up into the steering column and are fairly long. Mine are just dangling but being tightly twisted together something tells me they are a bit more important than just some small gauge wire. I couldn't find them on the wiring diagram, but could have easily missed them.

Black wires would be grounds if stock. I'll bet those are something someone added. Where do they connect?

 

[AzTaco]

Black wires would be grounds if stock. I'll bet those are something someone added. Where do they connect?

They lead up into the steering column. I haven't fully explored them yet. The ones I circled is what they look like, but I failed to see just above the blue twisted pair is a black/black-white twisted pair. It would be these wires possibly. I'll follow them to an origin.

 

[klhansen]

That whole mess looks aftermarket. I've never seen stock wiring twisted like that. Maybe a stereo or alarm installation. All the stock fuses are in the fuse panel, and I'm seeing a few inline fuse holders in your pic.