Possibly the latch mechanism is sticking in the 'unlatched' position. Happens a lot, particularly in icy regions like mine. With door open, use WD40 to clean mechanism, and get it to latch and unlatch freely using screwdriver to poke at it. Wait a few minutes for the bulk of the WD to evaporate or runoff, then spray mechanism with lithium grease.

My hood latch froze open last night...
Best of luck.

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1986 300E 5-Speed 240k mi.