The temperature just dropped here and one of the "project" cars did not want to crank this morning, early 80's 123 Wagon. I tried the normal things, pump the hand pump on the injection pump, extended wait time for the glow plugs-although the light was not coming on, I could hear the relay click. None of this worked. So I broke out the multi-meter. 4 of the 5 glow plugs were good at .7 to 1 ohm. One was open, obviously a bad one. Good continuity between the pins at the glow plug relay to each glow plug, 12V to the relay, 12V to each side of the large flat fuse in the relay. No voltage to the glow plugs while the relay was latched. So, the relay is not passing voltage through it even though I can hear it click on and click off.

Un-hooked the battery, 10 mm socket to remove the main power to the relay, pulled both pin and socket connectors off the relay and a 8 mm socket to removed the relay from the fender.

Take it into the garage and 4 small phillips head screws is all it takes to pull the cover off.

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Turbo300Mercede
87 300D W124
83 240D W123
80 300 TD Wagon W123, 4 Speed from 79 240D, SLS Rear Suspension