2005 F-250 SRW, single alternator, new batteries
Took the truck out for a spin the other night and figured I'd get into it a little and clear everything out since it'd been sitting for a few days. As I pulled away from an intersection at 3/4 throttle, I hit ~3800 rpms and just as the truck was shifting into 3rd gear my battery light came on and stayed on. I looked down at my ScanGaugeII and it was showing 11.8v. Awesome. Pulled over on the side of the road to make sure no connections had come loose and everything looked okay and I drove home (3 miles).
Got home and checked the voltage on the alternator (red lead to threaded stud on back of alternator, black to grounding point on the fender) and it was reading 12v or less. Checked all my fuses under the hood (driver side fuse holder) and all the fuses in the dash and all were good. I just replaced my batteries with a pair of DieHard Platinums
a few weeks earlier, and even before those were replaced I'd always see 13.5 - 14.0v on the ScanGuageII when the truck was running. Talked to a couple of people and started a thread on another site and the consensus was that my alternator died (it was a 3-4 year old large case 200a unit from alternatorparts). Ordered a 220a unit from DB Electric and installed it last night......aaaaaaand I'm still at 12v or less on the ScanGuageII. Began troubleshooting and here's where I'm at:
-- Still reading 12v or less off the threaded stud on the back of the alternator
-- Battery light comes on with KOEO, and goes out when I start the truck (voltage is around 12.6 - 13.0 at idle after the glow plugs finish their cycle)
-- Disconnected batteries and each read 12.3v (keep in mind I haven't re-charged the batteries since the night of the problem)
-- With everything connected, I'm reading 0.3v from the threaded stud on the back of the alternator to the positive terminal of the passenger battery, so I know I'm not losing voltage across that wire)
-- I unplugged the three pin / two wire connector from the alternator, started the truck, and check for voltage on both pins: 11.74v on one, and 12.0v on the other
-- Double checked all the fuses in the engine and under the dash again, just in case
As of now, the only two things I haven't checked are the amp output of the alternator and load tested the batteries.
Other than these two things, what else could I be missing?