John:

If the battery would crank the engine, it would run the GP relay.

The temp senor is on the relay itself, not separate.

Try testing the resistance of each plug again at the plug, but if you have 0.6-0.8 opm, they should be fine.

From here it's up to you -- either spring for a new set of glow plugs and hope, or get a new relay, it sounds as if the circuit is bad and dropping it off line too fast. You can verify this by having someone switch the "ignition" on while you have the meter attached. If you get transient voltage, replace the relay, the temp sensing circuit is bad.

Peter

__________________
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!