So tonight i just finished a cluster gauge install and took it for a spin. get a mile down the road in over drive 65 mph starts surging shut the overdrive off stops turn it back on starts again set the cruise still did it. go back to the shop take DMM reads .041 AcVolts. so then i started thinking that im not sure if it has ever been jumpy it with my lights off so i turn on headed lights which by the way are HID'S and it reads .72 then i turn on my PIAA fog lights two sets of them and reads .93 turn everything off goes down around .041 differently ac voltage being read.first question can testing at the batteries pic up ac voltage from other sources besides alternator?My thought here is that these lights have a pack that came with them that turns up the voltage (not 100% sure thats what they do) i think they might be feeding ac current back to the batteries then feeding from there to other important components.Next question if this is really what is causing it is there a method of filtering that my work i really hate to lose the bright light (i really love them ha)Next Problem my be related to the first one more then likely is.I was driving a two weeks ago dinging starts says check gauges i look alternator gauge shows its not charging dropped to 0. I pull over shut the truck off start it back up right away alternator gauge shows its charging fine. tonight (two weeks later almost to the day) when i was finishing up with cluster gauge install i was cycling lift pump to prime the system wasnt sure the fuel pressure gauge was reading right so i was starting truck letting it run for a min then shutting it off repeated this several times. then i left it run and was checking for fuel leaks i heard the dinging again. same thing alternator gauge said 0 volts.I installed this alternator on Dec 31 2012 so coming up on a year. when i replaced the old one it was doing the same thing took the old one to a well trusted starter and alternator re-builder he tested it and it was doing some crazy things. he said hes never seen anything like this before.I would have had these lights installed about the same time period on the first alternator as i have on the second one (around a year a piece on each alternator)My question on this part is. Is it possible to be back feeding AC voltage from these lights into the battery then to alternator and causing them to fail. If so what else could i be damaging.Not sure if all the text between the questions was necessary but trying to say what im thinking and catch you guys up. any thought or input will be greatly appreciated

Most likely the diodes are just cheap as you adding load to the electrical system the diodes start to heat up and fail. Just because the alternator was bought new doesn't mean its a quality unit either. I've seen reports of brand new alternators failing the AC test out of the box. I would have the alternator serviced at that alternator shop and have it done right. You might disconnect the alternator all together (field and alternator fuse) and test again with headlights on and see if the HIDs are generating the AC noise.