Junction block eh?

Is this perhaps the one with 3 phillips screws? 2 big ones and one small one?
I removed the screws and cleaned it up, reassembled, tested again, I still get 9.3ish volts when glow plugs are energized at the relay, at that terminal block i get 10.9v

I tried swapping batteries just in case i had a weak cell or something.
No go there, same exact situation.

What I'm curious about is if the PO has hacked into the glow plug power wire for the fuse panel, or possibly the radio or something idiotic, as the fuse box on the drivers side also drops to 9.3v when glow plugs are energized.

Do you know if the wire that powers the relay is visible up under the dash anywhere?

I'm going to go run a heavy gauge jumper wire from the battery to the relay and see if i get voltage drop and hard start then (No, I'm not going to leave it like that, this car is for my wife, I'm not doing a hack job like that and leaving her stranded somewhere)

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1982 300D (w123, "Grey Car")
1982 300D (w123, "Blue Car")
2001 Ford F150 "Clifford" (The Big Red Truck)
1997 Dodge Ram 2500 12V Cummins
1996 Dodge Ram 2500 12V Cummins
Previous Vehicles:
1995 E300D, 1980 300SD, 1992 Buick Century, 2005 Saturn Ion

The wire that powers the relay should not go through the firewall/ under the dash if it is factory. Running a heavy gauge jumper wire from the battery to relay is a good test, but that is only half of the equation. The ground strap is the other half, so make sure that is OK also.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I will take some pictures tomorrow, it looks factory under the hood, some other things have been a bit butchered though. I'm realizing why it was $1300 with help from my wallet...

I'll also check the ground strap.

With the jumper wire, voltage stayed at the expected 11ish volts at the relay. I will do more with it tomorrow and hopefully the weather will be a tad better.

Thanks for the help guys!
I'll report back with pictures and stuff!

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1982 300D (w123, "Grey Car")
1982 300D (w123, "Blue Car")
2001 Ford F150 "Clifford" (The Big Red Truck)
1997 Dodge Ram 2500 12V Cummins
1996 Dodge Ram 2500 12V Cummins
Previous Vehicles:
1995 E300D, 1980 300SD, 1992 Buick Century, 2005 Saturn Ion