Hi again!

You might want to look at this legend on the 2.2 ECU.
It may display what it is doing to your relay.

http://www.injectronics.com.au/assets/Uploads/InjectronicsTechnicalBulletin39.pdf

The relay diagram I linked you to, in another thread post of yours, is showing the system relay not energized.
Note: FYI.... On most schematics, unless otherwise noted, they always show relays displayed in their non-energized or not turned on mode.

Note also that the key "O" is the off position in the schematic.
That red line should always be hot and show voltage.
That red wire give power to "both" upper contacts that will close. A small detail to note.

Pass the ignition key, things will have to turned "on" to make current go around. But it will still stop until something closes a circuit to ground or connects another wire on another wire.

The ECU is lots of cases is going to being that "something" related to the injectors and so forth.

In theory class about electrons, I think can be considered labeled backwards to me, Says, the ground power is the one side looking for a place to go back home on. That power goes from negative to positive. Backwards to my checkbook too!

But I have reasoned it this way. (:)
Grounds are very important as they are half the circuit with no moving parts.
Since grounds don't move much, I think, that it's the main reason their points get the greener or white cruddy stuff first.
Just a theory, without proof, unless you see moss on dead logs. (:)

Looking at both links mentioned,
Pay attention to pins 9 and 21 of what happens when that side of the relay closes over to the Orange wire. This is Arts favorite test check point because it is easy to get too.

Pay attention to pins 17 & 18 or the wiring in between.

I'm not sure but in the pin out diagram it makes a reference to a (464) relay. I think it might be built inside the ECU.
This relay maybe controlled by seeing the distributors ignition signal. If the car runs that should not be a concern.

I do not have access to the Volvo problem solver directions that you are referring too.
The one I did find :
http://www.volvowiringdiagrams.com/volvo/Trouble%20Shooting%20Guides/Volvo%20Problem%20Solver%20Advanced%20Edition-1.pdf

Is not correct for your age car as it is talking about two separated relays used on '84 and earlier cars.
Yours is combined so it is sharing terminals to do the same thing ...only.... Differently, because they can.


Now that I'm past the confusion presented, we are back to those Darn test light questions.
It appears to me that the two test lights are operating under two different methods of exhibiting light as an indicator.
All the while, you are saying, One operates the relay and the other one does not.

The home made one you said is using a light bulb. The bulb lights is passing a massive amount of current through it to make the filament glow.

The store purchased light was not described to be an LED or incandescent.I'm guessing it's a LED test light and is safer to use, like a voltmeter, around electronic circuits.
It will not pass excessive current and overheat something like an electronic component.

In either case, it's about current flow. The latter uses almost "nil" current when compared to the incandescent. It has a limiting resistance value to drop the voltage down to 2.2 volts for the LED.

You will need to pass some current or at least enough to create a magnetic field to close the relay.
The LED should not be able to close the mechanical relay. An LED draws only about 20 + milliamperes. The coils in this relay might need ten times that, as a guess.

Depending on the bulb size and the "voltage drop" incurred "where" decides if the relay works or not and if the bulb will light or not. That's what is happening in your case.

One reason is the coil can limit the current through the bulb, yet that the relay closes, but can create a very dimly lit bulb due to that lower voltage.

In both cases, you are talking of a current limiter or resistor of different proportions and the result are... "Your results, without a doubt, will vary." Light on or off or dimly lit and may not be seen but completes a circuit.

Electricity operates on the inverse of one to another. The rise of one, say "voltage," can make the other, say "amperage," to fall. But something called "wattage" is there to make the figures come out right in energy use calculations.

Now, you wonder why is he telling me this?
All three words have a word "age" in them. When you figure all this out.... You will be little bit older? (:-)

There you go, ?????? Study a little, play a little and learn a lot about the world around us.

Is not going away, in fact, it's a smaller faster world due to it.

Are you using a bench setup or the cars battery circuits?
The type or size of battery could make a difference depending on the incandescent bulbs.
I Just needed to ask?

Phil