I'd get a 6V battery and coil, put them in observing the correct polarity and then see what works and what doesn't. It's a pretty basic electrical system... Likely failures would be the alternator diodes (it may have a generator, which would be more robust I think), voltage regulator, fuses, any bulbs that were lit up (brightly for a second or two!), blower motor, and I think that's about it. Starter would probably survive a few brief attempts.

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1987 W201 190D