Problem with brake lights not staying on

1994 Chevy C1500 pickup. Brake lights flicker when pedal is pushed, but only stay on when brake pedal is about halfway down. Both turn signals work and hazards work fine. We've checked the wire going in to the brake switch and it's good. Could this be a faulty brake switch? Any other suggestions of what to look for before we buy a new switch and mess with replacing the existing one?

I watched an online tutorial about replacing the switch before I came here, but before I crawl under the dash and start disassembling things, I'd like to make sure I'm not overlooking something easier or more obvious.

I don't know if it's relevant or not, but the pickup has been sitting for about 6 years. We're trying to get the old girl up and running for our son to drive.