Negative Voltage From Ecu? (surging Idle, Won't Start)

Any idea why when I measure the orange (or white with orange stripe) voltage reference wire at my TPS, EGR and Barometric Pressure sensor it reads as such:
TPS: +.5
EGR: -.5
MAP/BP: -.5

Yes, that is negative. Why?

I noticed that somehow the wires cross at the connector between the EGR and TPS and I unplugged the TPS, but the EGR and BP still read NEGATIVE voltage. I have owned this car 11 years and not modified these wires.

I checked the black w/white stripe ground wire, and the grounds in the engine bay, and all are under 1 ohms.

My computer is stock A9L. No engine mods. The TPS has exposed wiring so I have bought a new one. However, putting a brand new sensor onto a line that's sending negative voltage seems like possibly a bad idea, right?

My codes were 34 and 63 with KOEO, both C and O. The TPS is below 1.0v on the green wire. I pulled the EGR and it was gunked with carbon so I've cleaned that and the IAB. The negative voltage baffles me though. Why negative voltage?

Thanks, you helped me realize what's going on here. It turns out that for some reason the wires are opposite colors on my harness. My white/orange is the ground and the black/white is the 5v reference wire. So if I read the + on black and the - on white/orange I get a +5v. If I read them the opposite (how they're supposed to be read) then I get the -5v. How odd! As far as I know this is a factory harness. Anybody else ever seen this?