Just as the connecting hook makes contact thereby sending 1.21 gigawatts into the flux capacitor...

9 seconds sound clip from the Back to the Future movie soundboard.

You can hear this line at 01:09:35 in the Blu-ray version of the movie.

Quote context

[...]

- It's good. Oh, thank you. Thank you.

- Okay, now. We run some industrial-strength electrical cable from the top of the clock tower down, suspending it over the street between these two lamp posts.

- Meanwhile, we've outfitted the time vehicle with this big pole and hook, which runs directly into the flux capacitor.

- At the calculated moment, you start off from down the street, driving directly toward the cable, accelerating to 88 miles per hour.

- According to the flyer, at precisely 10:04 p.m. this Saturday night, lightning will strike the clock tower, electrifying the cable...

- Just as the connecting hook makes contact thereby sending 1.21 gigawatts into the flux capacitor...

- And sending you back to 1985.

- All right, now. Watch this.

- You wind up the car and release it.

- I'll simulate the lightning.

[...]