The pump relay is under the ECC on the front wall of the engine compartment behind the passenger headlight. There are actually two relays and switch down there in a really hard to reach spot. I thought I had the relay in hand only to find out that there was another there. If I remember correctly the pump relay is the one to the outside of hte vehicle.
I would definately NOT suspect this relay but would think that the power wire may have been a good suspect as it was a sudden stop as you mentioned without hard vibrations like running through potholes or something of that sort.
Is there anything else you did under the hood the day it died?

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique