It has been in the high 50's today. After letting the car cool down as much as it could I started it. The glow plug cycle seemed normal and the engine fired right away. After running for 3-5 seconds the GP light comes back on. I can not imagine that more than one is out, but that surely does not line up with my multi meter readings.

Note: the battery was changed about 18 months ago.

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Current:
1985 300D aka Miss Margaret
1991 300SE aka Alarice
1995 SL320 aka Samantha
1997 K1500 Silverado
Past:
1999 E300 ex-wife got it and let her son ruin it
1984 190 2.3 ex-wife got it and let her son destroy a great car
1985 300D (CA version) aka Maybelline lost to deer at high speed.
1981 300D aka Madeline (went to salvage at near 400k) rusty, yet best car I ever drove
Wishlist:
McFarlan TV6 (only a few privately owned)
ReVere with Rochester engine
1917 Premier (only one left)