Oil lamps usually illuminate OK.. did you check it when the engine had just been running? If so, chances are much oil was still around the valves etc. - they read lower on the dipstick than when the engine's cold

later

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190E's:
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black 2nd owner
http://www.maylane.demon.co.uk/190esmall.jpghttp://www.maylane.demon.co.uk/190esmall2.jpg