Fuel pump runs with direct 12V, but not otherwise

My 1992 Porsche 968 track car's fuel pump is behaving strangely.  Normally, it turns on when the fuel pump relay is energized when the key is turned to the start position.  Alternatively, the fuel pump relay can be removed, and the appropriate terminals jumpered, which turns the pump on immediately.  I recently replaced the fuel pump with a new Bosch unit because the old one leaked, and it ran fine at its first track session, but then suddenly stopped working.  So I tried applying 12V directly to the pump's electrical connectors from the battery via jumper cables and alligator connectors, and that never fails to turn the pump on.  The wires and their connectors look fine, as is the fuel pump sender fuse.  Any idea what can cause a pump which runs fine when 12V are applied directly to it not to work when the signal comes through the normal channels from the battery, through the relay, to the pump?  Thanks.

So, if I read this correctly, you can power the pump via jumpers to the terminals at the relay, but the relay won't energise it.  If so, either the relay is not being energised, or it has failed internally.  If it's not being energised, you have a bad connection, a bad relay, a bad ecu, or no spark.

Sounds to me like a bad relay. That seems like the obvious explanation. Any reason to think it’s anything else?

I'm curious how the old fuel pump leaked...

Test the relay. 

Ck the ground on the relay

Simpler than that, check for 12vdc coming to the relay, if you have bolts at the relay in, but not out, it’s a bad relay. And they DO fail! Relays are capable of working and not working. I’ve seen it a million times. They can even ohm out correctly across the windings and STILL work when cold, and not when hot. 

I would wire  in a new relay, if that doesn’t fix it, jump two wires to a volt gauge and monitor when you lose 12vdc. At that point it’ll be a wire break or a bad ecu

If the relay is not the culprit, could be an efi sensor. Some ecus will not fire the fuel pump unless they see engine cranking/spinning, etc. 

I assume it is not a return-less system?

Also, love the screen name!