How do I stop the Magrathean missiles from blasting the Heart of Gold

Hint 1 of 4:

Maybe Eddie needs some help from an unlikely source?

Hint 2 of 4:

Remember anything reserved for emergency?  This is an emergency!

Hint 3 of 4:

Put the large plug into the large recepticle.

Hint 4 of 4:

Flip the switch.