What would cause the fuel pump to constantly run - even with the engine off and no key in the ignition?

Just changed the oil & filter on my 1988 Turbo (Shiro) and took it out for a nice spirited drive. Ran great. Came home, parked the car, walked aournd it, and as I walked by the rear, heard the fuel pump humming. Waited a few minutes - never stopped. Finally just had to pull the negative off the battery.

Went out a few hours later, put the negative back on the battery - and heard the pump running (so disconnected it again). Weird.

I haven't had a chance to dive in and investigate- but plan to soon. Where should I start? Fuel pump relay?

ShiroCran