I'm not a moron, thank you very much. I think I'm capable of putting a test light on a gp relay. If You feel it's necessary to subtly insult, ill pass. The glow plug relay works because the glow plug light comes on. Ill do it anywAy

The GP light comes on during start up "Testing"
The GP Light has a "Fault " sequence that alerts the operator .
(Also what you call "On")
The GP light CAN tell you about "After Glow"

You can test for continuity/Amperage/Voltage @ the 5 pole plug or at the individual GP s .
But for any except continuity you've gotta "See"what the system delivers to each Plug.

"Dash Lights"(Instrument Cluster) are simply an Amusement Stuttgart provides
because it lends some credence to who's actually in control as you blast down
the Interstate.

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'84 300SD sold
124.128

When he said the GP relay is "working" I assume he meant he heard the relay clicked when the key was turned to glow, the glow lamp in the cluster went on and then off with another click indicating the glow cycle was complete, and he was able to start the engine without having to crank it for more than a revolution or 2. Is that not enough proof that the GP relay is working?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

"Peer Repeatable (Scientific) Proof Positive"

After everything he put HIMSELF through, even with the enormous amount of
assistance received... Acquiesce in anybody's Assumptions IS Enablement.

It's his MB (MMV)
Just like Yours belongs to You. (Mileage May Vary)

AND you're free to do whatever you want with the chassis.

Proof of the GP Relay "Working" properly would be the Voltage / Amperage and
Duration of each as delivered to the Glow Plugs.When computed against Ambient.
(Most Especially in this case!)

BUT,as OP states he Happy to be able to start and operate His MB...

Implied is, "Anything else is just a Bother."
As am I for making the suggestion.

__________________
'84 300SD sold
124.128