Help wiring magnafuel external fuel pump in cobra

[jedpony]

Hey guys, ive got a 96 cobra with a glens sumped fuel tank and magnafuel mp4303 fuel pump. Im running a relay and 30 amp circuit breaker. I have 8 gauge wire running to supply the pump with power and im using the ignition on off switch wire in the back of the trunk to tell the pump to turn on when the key turns on. For some reason with it wired this way the fuel pump primes and starts but only stays running for a few seconds until fuel pressure drops to zero and the car shuts off. Do i need to tap in the ignition switch further up in the car before the emergency shut off switch in the trunk? Ive checked all my connections and grounds and they are all good. Surly its something to do with the ignition wire i tapped into?