It is a pulseing signal from the Ignition module that makes and keeps the FP relay energized. Disconnect the plugs/conectors from the ignition module and see if the pumps stop. If not, and I don't think it will, remove the FP relay and make sure they stop. If they do, probably the relay is bad. If not, there is a short somewhere. Look at the FP relay socket and make sure someone didn't put a jumper wire in to make the pumps stay on.
Let me know what you find.
84 500 SEL (307,xxx miles)