Thanks for providing the solution.
I think the ground resistance was dropping the unloaded pin voltage from the 12.46 to 10.98 volts you measured.

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1985 300D Turbo
"Evolution is God's way of giving upgrades" Francis Collins

Appears the newer glow plug circuits develop faults not too common on their earlier cars. Most that have read this thread will remember that their designed ground is questionable now. Your experience has probably increased common knowledge on that model.

I'm looking at the Wiring Diagram for the GP relay right now,in search of the
ground wire!
'Got it! Terminal 31 on the Pre-Glow Relay provides Ground to W3 (At Driver's
front wheelhouse)

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'84 300SD sold
124.128

Just for clarity in case someone else has the problem. They appear to have soldered a wire into one of the connectors on the relay (I haven't pulled the cap off to inspect their work). I believe it is the smaller connector not the leads to the gps. The just ran a new wire from there to the frame down below the fender area rather than try to hunt down the break in the old wire. Made sense to me. Car is working like a champ now. Cost was less than $100 to find it and fix it.

It's hilarious to hear you guys mention my car as one of the 'newer' styles. This one is 17 years old. I just rolled 100K a month ago so I hope she has a long life ahead. There is nothing like driving this thing. I rented a new Chevy Equinox SUV for a recent work trip. My 17 year old 300D was in a different class than the new SUV. Not even comparable to ride or feel. The same goes for my 02 F150. I don't know if the real new ones have the same feel but this car is awesome. My wife's E320 wagon (95 model) has a heavy feel but not like my 93 300D even though the bodies are similar.