Water in the wiring caused the tach flicker, I'd bet.

The lack of a glow plug light means you have iether a burned out dash bulb or several bad glow plugs. This can mean bad wire or connections, too, by the way, the sensor reads current draw.

Take the wires off the glowplugs and check the resistance to the block of each -- they should be 0.8 ohm or close. If one shows open or zero, replace them all, they aren't that expensive and are easy to replace. You can also pull the plug on the relay and test from there, too.

If they are all nominally good, check to see that the relay clicks when you turn on the key and that you have voltage (usually 11 V or so) at the glow plugs. Check them all, and if they all don't, it's relay time. If some do and some don't, the wires are bad (not very common).

If you have one GP out, the light either comes on and blinks after you start, or stays off until you start, then blinks. More than two, and it usually doesn't come on at all.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!