Engine is having trouble starting cold and the glow plug light is not lighting. I have tested the plugs with a multimeter, some seem ok, some questionable, but I am unconvinced of the accuracy of these results; the internal resistance of the multimeter itself is at least .6 ohms, and that jumps a lot, so I don't trust it. But I'm rambling..

I want to pull the plugs so I can apply voltage to them and test visually, but when I put my hand anywhere near my engine, I'm covered in grease from head to toe. I want to degrease the engine and glow plugs a bit before I try to get the plugs out. I've read to take precautions like cover transmission vent and electronics, make sure engine isn't hot when washing, and check vac lines afterwards, but is it ok to spray degreaser/water directly on the plugs and wires around them?

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1983 Mercedes 300D Turbo / 268k miles

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