first time i have to pay for work

[68w/sbc406]

so i changed my truck over to a internally regulated alternator and added some electrical stuff, and my alternator went out(still charged but drew power when the ignition was off) so i bought a new alternator, well my truck had a dead battery again (6 months after i bought my alternator) and in the frist case my radio kept flickering on and off, and it does it again now. so i take it down to the electrical shop that gave me advice about what wires to move when i did the new style alternator and they checked one of the wires that plugs into the back of the alternator and it was hot with the key off. they said that something i put in i tapped into that wire and was some how making it a constant instead of a switched. i told them that i didnt and we went thought a couple of easy fixes and the stuff i did and put in and couldnt find anything that was wrong (cause i am perfect and didnt screw anything up) so i looked all over and couldnt find any problems so i am forced to take it down to the shop and pay the 74 an hour to have them fix it. they told me to be ready to spent around a 100 bucks. the only other time i have had to pay for labor on my truck is at the body shop.