You probably won't get it started without glowplugs at 40F -- mine is reluctant to start warm without the glowplugs, and intert when cold without them.

What I would do is be prepared for two problems -- a dead switch and one or more dead plugs.

Make up a heavy jumper with big alligator clips about two feet long. Make of large diameter wire, preferably solid copper rather than stranded -- it will need to carry 50 amps or so, plan on it getting hot. You can use this to jumper from the positive battery post to the back glowplug if the switch is bad. Don't leave it on more than a minute or so -- you can melt the glowplugs and cause them to fail.

Take two or three new plugs with you, and a proper sized wrench. That way you will have replacement plugs for any that are bad.

The 71 will have series plugs -- if one is bad, none of them work. You can check by looking at resistance between the lower collar were the wires go and the top collar were the screw is -- if there is no continuity, the plug is bad. You can also check for voltage at each wire connection between plugs with a voltmeter (or a screwdriver grounding the wires to the head!) while the glow plug switch is pulled.

Make sure you get the alternator light to dim slightly while pulling on the knob BEFORE the starter operates -- kinda hard to describe, easy to do once you get the hang of it. That spring is STRONG, and it is easy to not pull hard enough to close the contact properly. They also can fail and not run the plugs unless the starter is also engaged.

My guess is that the switch is bad, because it did start when cranked (the plugs stay on, without the dash resistor in the circuit). Jumper from battery to glowplugs for 30 sec or so, the crank. If it sparks when you connect, the glowplugs are fine.

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!