Where do I start looking for an electrical short?

A couple of weeks ago, we were FINALLY able to pass emissions for our F-100. Since then, however, our headlights & dashlights started going out. On my boyfriend's way to work, one of the 20amp fuses caught fire, fell to the floor board, then melted. He had a "friend", who is supposedly a master mechanic, look at it, but only made the situation worse. We do have headlights now & occasional dashlights, but now we have no lights to the tach, no radio, & no heater. Although, the radio & heater are "luxuries" here in Arizona, I'm afraid if not properly tended to, this short could cause even bigger problems, or worse, the loss of our only transportation. We've asked a few shops nearby for an approximate price range on getting it fixed & the general quote has been $100/hr not including parts. Although, I'm sure their skills in this matter are worth that, we are on an EXTREMELY fixed income & no WAY can we afford those prices. I do have SOME knowledge of electrical, but a point the right direction would be MORE than greatly appreciated. THANK YOU SO MUCH FOR YOUR TIME!

Tanya Worthen