I had a Ford Van do the same crappy thing to me....changed the battery as was sitting unused for some months....battery showed about ONE VOLT on the terminals....talking the lead posts now, not the wiring.....had a hell of a time beating the stupid security system, but finally got it to start....battery at 12 volts, alt dead, changed alt for a new one.....and so fine for a couple daze....dead battery, failed to start...towed to my driveway, put on charger, battery came back ok, being all I use now are Marine Deep Cycle batteries....
Alt not putting out, old one did test bad at parts house, I take new one back off and sure enough tests GOOD.....
so I start engine again it's idling away.....I checking voltages on fuses, and all sorts of crap....once again back to the battery....I just touch something on the + side of the clamp/wiring and it dies.....I pull all the crap apart, they had TWO heavy wires going to the stupid clamp, with a 10mm stud/bolt and so I pull that crap apart, and tons of stupid looking goop and corrosion because the goop didn't work.....scraped it all off down to naked metal all nice and shiney......used bearing grease on the two tabs and the stud/bolt....secured nicely, spread the grease around....and van starts/runs fine.....some damn nitwit runs a ~3/8" wire from the Alt stud to the battery post, then from there to the rest of the fuse/block/wiring of the van.....
WTF??? so that stud is subject to the corrosion of the battery fumes.....SAE all the way.....Stupid Assed Engineering....kid outta college with NO automotive experience doing shit he dunno shit about......
:clobbered::club: