I believe the lady's glow plug relay fuse has melted and her engine's
glow plugs are therefore not receiving any power. The glow plug relay
has a cover which slides UP to reveal the fuse or fusable link. A
replacement link costs about $1. Imagine, buying a M-B part for $1!

As to checking a glow plug, They should have some resistance BUT if they
do that doesn't prove that they're working, in my experience. I've
removed them and tested each with jumper wires from the battery - and
each quickly boiled water BUT one was still weak and had to be found by
elimination - install a new GP in #2 try it, no change, put old #2 into
#3 etc until the misfire problem was fixed.

First check the link.

When I removed the #3 glow plug and tested I did this with 12 volts and
the plug glowed cherry red in a few seconds indicating that it was
working fine. The reason I wanted to know if there was a way to check
while still in the circuit was because I can hardly get to the
connections and when I do the black plastic sleeve covering the wire
cracks and disintegrates. The hardest one to get to is the #5 plug as
it is stuffed back behind the oil filter and a b**tch to get to. I have
not checked the wiring diagram (don't have one) to see how these are
wired but they appear to be in parallel as there is an individual wire
running to each one from the same source. If parallel then 1 plug could
be bad without affecting the rest, can anyone confirm this? If they
were series connected then you could check for continuity from the
first to the last and then determine which one was your problem. My
guess is the relay and fuse must be OK as I get 12v to every glow plug.
I have an infrared thermometer on order to try and determone if the
plugs are working without removal, anyone have experience with these
and do you think my plan might work to test without disconnecting.
Currently the glow sequence starts and runs until the glow light turns
off and then continues for about 15 more seconds before shutting off
and the engine just turns over without firing. Could this be valve
related? Car runs like a scalded cat after I get it started, well maybe
not scalded but the turbo runs full time and will actually put down
rubber if I brake stall it. I can't get back to this problem until
after Jan 2 but will post my findings; until then, have a Happy New
Year everyone and thanks for the insight and input.
Doug in Sacramento