I have a 99 ford f350 7.3 that is not charging properly. Here is the jist of the situation:

I went on a trip to the Jersey shore a few weeks ago, when I noticed along the way that the battery gauge had dropped profusely to just below the white "OK" line. I bought the truck a few months ago from a roadside mechanic who had three batteries in the truck (he told me he used the third to jump other cars/trucks). thinking that the voltage of the three batteries combined may be too high, I quickly pulled over, popped the hood, and with the truck still running, disconnected the third battery. within roughly a minute, the battery meter was operating in the correct range (a little bit above midway of the "OK" area), and I continued on my way. The truck was fine until the return trip home when I noticed the voltage dropping again. I had recently replaced the alternator, so I popped the hood, and pressed down on the alternator pigtail (the clip on the pigtail that holds it into the alternator had snapped off during the swapping of the alternator). The battery gauge was again reading in the proper area. For the last week or so, if the battery reading would drop, i would simply pull over, press on the pigtail, and all was well again. but a few days ago, this tactic stopped working. I replaced the Alternator pigtail thinking that this would solve the problem, but when I charge the truck and start it up, the voltage continues to plummet. It may be important to mention that the new pigtail I put in has three wires coming out of it, and the one previously in the truck had two wires coming out of it. If anyone has any advice onto where or what my next step should be, or possibly (and better yet) a solution to said problem, It would be greatly appreciated. thank you in advance

 

today I tried disconnecting the third (white) ground wire coming off of the alternator pigtail. Once I got a jump from another truck, the truck started no problem, and the voltage was immediately in the correct region. But once I disconnected the jumper cables, the voltage dropped a little on the battery gauge, and when I tested the meter by turning on the truck's lights and wipers, the voltage dropped and did not go back up. so I once again am at wit's end. is the charging issue(s?) another problem? I read on another forum that the glow plugs can stay on and drain the battery. what method would I take to test that route? Please any at all advice is greatly appreciated!! Thank you!