OK, my brother got me this awesome little extech multimeter lead set, man that's handy. Clips on the leads kinda like in your picture. I clipped one lead to the relay, and went around poking with the other lead.

I got 0.3 ohms at the fuse labelled c, for the aux fans it said.
I got 0.4 ohms at the headlight switch terminal.
I got 0.4 ohms at a red wire on the terminal block with them disconnected.
I got 0.4 ohms at the battery positive with the terminal block connected.

That seems like reasonable figures to me.

I tried again with my test wire strung across the top of the engine, 12.4 key off, 10.7 key on glow active.

Without the test wire, 12.3 key off, 9.2 key on glow active.

Should I just make a permanent jumper wire?

__________________
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

Did you isolate (remove) the glow relay wire at the terminal block (like in my pic) when you took those measurements? If you did, then those measurements indicates that wire has been messed with.

__________________
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

Your resistance values are fine. However the glow plug system draws lots of current. Take a small wire brush and clean the surface of the terminals as well as the terminal blocks that they connect to at the connection near the coolant resevoir as well as the battery terminals themselves. If you can get to the grounds; clean them too. When you check resistance, you are effectively getting continuity from one pin sized spot at the terminal, but you need a good clean surface to transfer all of the current to the wire efficiently. If the contacts aren't clean, you will get a voltage drop and not get your desired voltage at the gp relay or the glow plugs. I wanna say my glow plugs were at 11.5 or better recently after changing my glow plugs.

If all of the wiring is unaltered, I believe that barring major corrosion within the terminal to wire contact area, shining up the surface areas should help tremendously.

On another note, you say the car won't start. In your jumpering effort, you might consider jumpering an easy to get to glow plug; probably #3; straight to the battery for 20 seconds or so and then cranking the motor. At least you'll then know your no start condition is definitively glow plug related....


Hope this helps.
Mike

Funola: I removed one set of wires, the other set seems unwilling to move, I am afraid of rounding the screw out, I might see if I have a terminal block on my spare motor and swap them tomorrow morning.

I highly suspect wiring has been tampered with. Most of the car was tampered with. Wish I'd been a little more careful when looking it over when I bought it.

But, bent tie rods, damaged undercarriage, bearings, hidden rust, sunroof leaks, improperly attached air filter housing, flex discs, trashed cooling system and now glow plugs aside, it wasn't that bad of a deal...

Masc:
The car starts and runs good, when its warm outside, but the colder it has gotten, the worse it starts, glow plugs were my first suspect as that's what always did it on my 116.

I haven't been able to start the car for a week or so now, all whilst making an attempt at diagnosing this issue.

With a jumper wire attached, the voltage is much better and the car started earlier, which makes me want to just permanently install the jumper wire...

But it obviously the entire car had been a hack job before, and since my wife has claimed it as hers now, I want it to be reliable and solve the problems rather than patch them.

__________________
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

I have identified the wire for you that goes between the glow relay and the terminal block. It should not go anywhere else per the FSM. To check if that's true, you have to disconnect both ends of that wire and buzz it out to battery + cable, or the hot side of all fuses. If you get a reading, someone has tampered with it and tapped into that wire. It doesn't hurt to add another wire in parallel, but if it were my car, I'd want to know if that wire has been tampered with.

Try a long nose vise grip or dikes on the screw. That's a #3 Phillips btw. Using a #2 bit is probably why it's rounded.

__________________
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

That's my sentiments also. I'll try getting some vice grips on there, I don't mind replacing the terminal block, if I can even break the screw off or drill it out I'll connect it all together temporarily and buy a new one.

I'll have a fight with it Here in a minute. I'd just like to know what has been done to the car. Id rather knowingly be driving a lemon (my 124 was given to me because of all the issues it had/has) and know its story than have a surprise a few hours from home.

__________________
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

Sorry guys, I haven't done anything more to the car yet.

My wife got into some poison ivy real bad, I'm not allergic so I've been helping her clean it and it's not getting much better, only been a couple days but we've got to go to the doc today and see if they can give her a shot or something for it, its all over her arms and its spreading...

Now that I'm done grossing everyone out, I'll be back on the car after she's better, she won't be driving it like this, she can barely bend her arms.

I'll keep you all posted on what I find out about my wire issue

__________________
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