You should try and check the relay before you replace it. You should turn the key on and listen in the area that the relay is located. You should here an audible click after about 30 seconds or so. My father's 82 SD did the same thing. I checked for the sound and knew that the relay was working. If its not the relay, its the plugs. We replaced the glow plugs (total cost was around $50) and its all good now. How old are the plugs in your car?

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2001 Dodge Ram 2500 Cummins Turbo Diesel - 4x4, auto, 3.54 gears, long bed
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'92 300D 2.5 Turbodiesel - sold
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