ilikechevy

i have a friend who has a 94 s-10 with a 4.3, 2wd long bed. the truck has a aftermarket sterio and amp in it. today i was trying to fix a few connectors on the amp. well after that i had to dig into the dash to check behind the radio, and when i was ready to pull the plastic piece that covers the entire instrument panel/radio area, i pressed on the brake pedal to shift the truck into a low gear and the truck's starter engaged and a relay clicking type sound started!!! what could be the problem? thanks for any and all help!!!