Electrical problems.. plz help me save money on this simple but dangerous problem?

i need help with my truck. i have a 99 dodge dakota v8 2wd with around 162,000 and let me tell you its nice and runs beautifully and really fast.i have had electrical problems with it in the past but it because of manufacture defects that all of the same make and year have after a number of miles but the problem im having with the truck is that every time i hit the brake my driving lights turn on and when 0i turn on my driving lights my 3rd brake light turns on. i have asked shops that deal with automotive electric but they will charge me $100 just to look at it and that's not including labor or parts. i don't know why its doing this i have replace my taillights and 3rd/cargo lights with LED with resistors. and replace my headlights and fog lights with 12k 35w hid's and my inside lights also with LED so in other words my trucks uses 3/5 less power which includes my sound system. and all this problems started to happen before we started getting snow, so its been sitting in the back yard for almost half a year.... plz help i would like to start taking out my truck before gas becomes more expensive then what it is.