I don't really have anything to offer as a solution, but since the post hasn't gotten any responses I will offer a similar experience with an injection relay buzzing.

I had a 240 that had the same no start and the injection relay buzzing. I was getting 12v from the feed wire. When I jumpered the fuses the pumps would run the relay didn't buzz and the car started.

As it turned out the wire from the battery that held the 25 amp fuse was corroded at the end that connects to the battery. The corrosion had worked its way up the wire under the insulation. I assume that the corrosion had increased the resistance in that wire that fed the fuel injection relay. It still carried enough current to register the voltage on the meter but there evidently wasn't enough current to operate the relay.

The 7/940 cars don't have that heavier fused wire from the battery to the relay. They do however have several additional wires coming off of the positive post clamp. Perhaps one of those feeds the relay in the tray??

At any rate I would remove the positive clamp and the wires attached to it. Give the additional wires attached there a good look for evidence of corrosion as well as the possibility of the insulation hiding corrosion.
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Any twenty minute job is just a broken bolt away from a three day ordeal