Ok. If it's warm out and your motor is in good shape it will start (eventually) without glow plugs.

As noted the 350 doesn't have a fuse on the GP relay, it has a self-resetting circuit breaker.

So you removed the intake. Did you block off the ports with anything when you did that? Is the stop lever free? If your vacuum has bled down it will go to the vertical position. If it's horizontal the engine will not start.

Watch my video here, you'll see the stop lever move up when I turn the key on : Mercedes 350 SDL Diesel S-Class Cold start - YouTube

I once bent the stop lever slightly while working in that area and it got stuck on one of the delivery valves preventing starting.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.