Vacuum is crucial to the starting/stopping of your engine. You cannot do it on electronics alone.

I know nothing of starting a MB diesel without a key (hot wiring), but imagine that it's not quite the easiest thing to do as there are many things you must account for (vacuum, electricity, steering wheel lock) all at the same time.

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-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon