As a first diagnostic step I would try locking and unlocking the door from the passenger side.

I think the alarm can keep the starter from working on that year. I presume that since jumping it didn't help that it isn't a battery problem.

Of course the final answer is to find the open in the circuit between the good starter and the good battery. It would be easiest if the open was the relay keeping the starter from engaging when the alarm is set.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician