>>Do these voltages look good

It's quite low, but as yet, it's difficult to tell if that's because the battery has gone West, or if there's a bad connection somewhere.

One way to tell is to repeat the test, but, put the positive wire onto the positive battery post (the post itself, not the terminal), and put the negative onto the glow plug 6mm nut. When the circuit is energised, you'll then measure the voltage dropped between the battery and the glow plug. If more than, say, 0.5 volts are being dropped, then, there's a bad connection somewhere.

If the voltage drop is OK, check the voltage across the battery posts while the glow plugs are energised - I would hope that the voltage would not drop to anywhere near 10 volts, which is a reasonable cranking voltage, not glow plugs as the only load.

I did measure the voltage across the battery when the glow plugs were on and it was around 10.5 volts. However, connection was made to the battery cable teminals, not the battery posts. I will charge up the battery tonight and do the test again tomorrow making sure I connect to the battery posts and also do the voltage drop test.

Glow plugs are all Bosch. They are pretty old and may not get as hot as new ones. I did not have nearly as much trouble starting it last winter. Maybe I also have a fuel issue (a bit of air) or starter motor issue or a combination of a little of each issue?

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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

A good working system should be at least 11 -12volts at each glow plug. make sure all the wiring is good and no corrioson. Did you check the glow plugs with an ohm meter?

just because they fine in terms of voltage doesnt mean there good. Ive pull 5 bad glow plugs out of cars that failed the ohm test and passed the voltage test.

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)