Can you elaborate more please.
"Voltmeter set to DC volts, red test lead to battery positive and black test lead to pin 85 on o2 and FP. Got 12v with key off."
Although this seems to make sense from a flow standpoint, matching red with positive and black with negative, it doesn't really give us what we're looking for.
We want to see if there is a 0v potential on 85, also known as ground. Well if the meter is reading 12v, then it isn't exactly showing us what we want to know.
Think of the red lead as the input. We want to check the circuit in question with the red lead as this is what the meter is displaying. So with your red lead on battery positive, it's showing you what the battery is at, when we what to know what the relay is at instead. We will move the red lead to pin 85 instead, since that's what we actually want to know.
Black lead generally always goes to a common ground point for easy understanding. This is our reference probe, and whatever it touches is considered 0v to the meter. So if we put the black probe on the positive battery post, 12v would be considered 0v, and poking the red lead at 12v would show 0v(no potential difference), while poking it to ground would show -12v, since ground(0v) is 12v lower then the reverence of 12v.
In short, Red is Input, Black is Ground reference.
Now, with that in mind, we still run into an annoying problem when checking grounds with the meter. The Meter will show 0v when nothing is connected, so how can we tell if it's actually nothing, or if we have a 0v ground? Usually when you are checking a circuit it won't be perfect so a very slight stray voltage will be detected, so if for instance we check pin 85 and it reads like 0.5v then we can tell the it has some sort of connection to ground.
The more prefered way is a resistance or continuity check. Since we can't see a voltage difference, we can instead measure how much resistance there is between the 2 ground points and infer a connection that way. A Reading of OL would mean an open circuit so no ground, where < 2Ω would show we have a pretty good ground path there.
You mean o2 relay to o2 holder?
The heater relay output voltage going to the o2 sensor, that big orange wire that started this whole thread, haha. Is it still stuck on all the time with the o2 relay properly hooked up to the fuel pump relay?