Fuel Pump Relay
With a cheap soldering gun, you can do a permanent fix on the relay.
The cover on the relay pops off. You'll find two solenoids, on the bottom near the pins.
The LARGER of the two is your fuel pump relay. Over the years the vibaration on the support(ground) piece has cracked the solder joint.
With a little flux and a hot solder gun/ solder, re-solder that joint on the back side.
Be careful not to solder adjacent circuits together. ZAP!!
Put the cover back on.
I did my '85 500SEC this way. Much better than a jump.
Good luck. Regards, John F