How much stuff do I have to get out of the way to remove GPs on '93 300D?
 

I can't see any way to get to them without taking the intake manifold out. I'll ream the holes so I need a little room to work. If so how much difficulty to remove the manifold and what else needs to be taken off? While I'm asking, how should I test the plugs (other than with an ohm meter which I hear isn't that reliable)?

testing them with an ohmmeter is OK should be 1ohm or less,the best test is to connect them to a battery and see them get hot,but be careful they get really hot quick if they are good,of course that requires that you have them out already.The ohm test is probably the best you can do before you remove them.Assuming your 93 is a 2.5 they can be removed without removing the intake,not easy but if you have 1/4" drive set with a u-joint and a 10mm socket and a 12mm deep socket,good dexterity and some patience you can do it. Don

I've had two fail, #1 and #4. I was able to get mine out easily with a 1/4" drive socket and deep well sockets. It looks to me that I can do the same for the others too.

I did not ream the openings.

I used an OHM meter to check mine. The bad GP was obvious because it showed to be an open circuit. I checked from the glow plug relay connection and the double checked it from the terminal of the glow plug.

After the first GP died I got a little smarter and bought 5 so that I would have the part readily available when I needed it.:eek:

I checked the resistance of the glow plugs at the connector to the controller and they were all under 1 ohm. I hear thats not a true indication of how they work under load so I want to test them out of the car. The car starts fine but the indicator light doesn't come on and it's not the bulb.

Get used to removing/installing the intake manifold if you plan on keeping the car and doing your own work. There is really not much to it. I always use blue Loctite on the intake manifold and you do not want to over-tighten them.

I don't plan on keeping it and I do my own work. I just want everything right before selling it.

Allen heads
 

If your 2.5 is a lot like the old 603, they have allen head bolts attaching the intake to the head. I found having a set of long allen wrenches with ball ends ( to allow some offset to the bolt ) was helpful. You may have better access on yours, but take a look before starting. The rest is just a lot of small parts to keep track of. Maybe take a picture or two to help reassemble.

If they're all under an ohm, they're all good. GPs are like light bulbs...they are either good or burn out. Burned out is infinite resistance...good is down near an ohm.

Then why won't the light come on?

You check the Bulb in the Instrument cluster?
 

The DMM Always tells the Truth.