Jim, you can't have one bad plug. The engine won't start. One plug won't prevent a start. On a six cylinder, two bad plugs probably won't prevent a start. So, the problem is with the relay. Either it's not getting a signal from the ignition switch, or the fuse is bad, or the relay itself is bad.

Testing glow plugs won't solve this issue.

Have a look to make sure the mechanic did not disloge the time sensor plug in on the block. It is a refference for the relay to indicate how long for it to stay on. It is the most probable thing in your situation that was disturbed by that mechanic. Take a look at the sensor itself to acertain if he hit it with the manifold as well and damaged the tip of the sensor itself. If the location of it makes it a possibility.
I just am not sure if the glow plug cycle is longer or shorter with it disconnected. If anyone states longer you might discard the suggestion for now and maybe not. I believe it is on the same side of the block as your glow plugs and manifold that is why the probability is greater. Others will have to tell you exactley where it is. Thats if the actual location makes it a possibility.
If under the manifold on your design you might use a mirror to check. All I really know is that I would at least check it out. Especially again if anyone states the glow plug time interval is much shorter to non existant with it disconnected.
Mainly since this mechanic appears sloppy and not very skilled also follow that wire to make sure he did not pinch it in the manifold for example. Not a great effort before continuing. The shorting out of that sensor wire might also cause a very short to non existant glow relay cycle to occur. The short could even have a semi intermittent nature to complicate this problem of sometimes there sometimes not. So two distinct possibilities exist there. At least in my mind.
From the electrical perspective sometimes it is an aid to draw the basic circuit as you understand it on paper.
I am not trying to unreasonably complicate this problem for you rather just mentally examining what could have occured. If the relay was cycling properly and activating the glow plugs reliabily before he changed the glow plugs. It will probably turn out to be something else but do not totally ignore this suggestion. It is very easy and not time intensive to have a quick look just to eliminate it.

I don't think the plugs themselves would have an intermittent problem and it seems the relay is working.

Maybe a bad bulb in the dash and 1 or 2 bad glow-plugs or glow-plug wiring.

Don

__________________
1980 300TD-T (82 Turbo and Trans) 159,000 Miles "Jackie-O"
1983 300SD 272,000 Miles "Aristotle"
1987 Jeep Wagoneer Limited - keeps the MB's off the ice and out of the snow
1994 BMW 530it

I checked the fuse at both ends and got 12 volts.

When I checked the GPs and got no voltage it was
on GPs 1-3.

Babymog...
I've been through the bent fuel lines/broken clips
scenario before. That was after my first GP change
and may have been my first post to this forum.

Halfway from Pittsburgh to Cleveland I had diesel
covering my engine!

I know already I'm going to have to replace them.
If not, it's just a matter and time and road vibration.

"part changer"... thanks. I needed a term for him
that's suitable for posting on a public forum.
On a pubic forum... I know the term.

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k. darkman
1987 300D Turbo 200k

Just to be sure:

1) Are you positively making the voltage check immediately after turning the key to the #2 position? No delay........immediate check of the meter (requires two persons)??

2) Are you positive that the plug for the glow plugs is definitely inserted into the side of the glow plug relay?


If the answer to both of the above questions is affirmative, then please pull the plug on the side of the relay for the glow plugs and perform the exact same voltage test on one of the pins in the relay. Immediately upon turning the key to the #2 position, check for voltage at one of those pins.

And, a final question:

3) Have you replaced the fuse yet?

I performed the 2 person test. Got nothing again.
I haven't replaced the fuse.

Just got back from A-zone. On the phone they said they
had it, but it wasn't what we need. Tomorrow I can
get one from the dealer.

Clear me up on the relay. That is the plastic case that
houses the fuse-- right?

There are two cables running in/out both ends. The one furthest
from the firewall attaches to the glow plugs. Am I looking for
something else?

Pins???
O.K. I looked at the wiring diagram
It shows X26 plug connector 12-pin
Is this what I'm looking for? If so, where is it?

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k. darkman
1987 300D Turbo 200k

Correct.

Nope, just pull the plug that goes to the glow plugs. In the relay, where the plug was removed, will be a set of pins. I want you to repeat the test using one or two of the pins.

Thanks. Have to wait for morning (when it's light).
I'll have the fuse then too.
Will check back then.

__________________
k. darkman
1987 300D Turbo 200k