voltage

it's built in.

 

TruckersWife319, it's all built in. I'm going to take a while leap here and suggest you are having issues in charging system? Before you answer that may I suggest you do sometime before suggesting a failing alternator. First clean all battery connections and cables especially cables going to ground and frame rails. Check cables and check tightness of cables to starter. Next on your fire wall next to air cleaner housing of passenger side of cab, check and clean cables at the main fuse (long strip about 2.5" long behind rubber cover), and solenoid. Check cables and tightness at alternator. The most important part of electrical system are the grounds. That includes grounding from batteries to frame rails, frame rails to engine block, engine block to starter, and any grounding cable from frame, engine, or starter leading to cab body. A dirty grounding system will cause voltage issues almost 100% of the time. Go through your truck and clean all cables and particular attention to ALL ground points especially leading to cab body. One bad ground cable connection will cause 50-things to appear to fail. If your engine appears to run erratic, verify both positive and negative wires coming from the ECM to battery are clean and tight. It's all about clean and tight wire and cable connections.