Truck is an '07, 4.6 with approx. 104,000 miles. About a year ago I had the alternator replaced after it failed. During the past couple weeks the charging system has gone haywire with the gauge almost pegging to the max indicating an overcharge situation. When it has done this I pulled over, put the truck in park & shut down the engine. The truck then starts right back up & runs fine. It's not throwing a code. Last nite during a short trip for gas, the headlights got brighter for a second & the gauge pointer just barely moved to the right. Today, I'm calling the shop that replaced the alt. Thing is, like I said it's not throwing a code. Will the shop be able to nail this down if it's not throwing a code?