Battery Light on w/ New OEM Alt and New Battery?
 

For at least a couple years now, my battery light has been coming on pretty often. I've been riding around like that up until recently when i put a new intake manifold on the ol' 2V (infamous coolant leak) and i put a new alternator on her too thinking it would fix the problem (battery on a trickle charger before going back in). Battery light would still come on after that but since the alternator was new (refurb'ed Motorcraft 130 amp) i didn't really think much of the light. One night i was at the drive through and my dash went dim, gauge cluster lit up like a xmas tree and eventually left me on the side of the freeway. Haven't really driven it a whole lot since then as i don't have all the time in the world to properly go through it. Recently put a new battery in it thinking maybe the "old" one was the culprit. Battery light still comes on. Cleaned the 3-4 chassis grounds in the engine bay as well as the actual engine to chassis ground near the oil filter. Light still comes on and off. Serpentine belt still has good tension and isn't cracked, although it is pretty old. Volt meter reads proper voltages at idle and @ RPM under load. Sorta lost...ideas?

i wouldnt write off the "new" alternator being faulty. Ive had plenty of parts be bad directly out of the box before.

Several possibilities here. I too have had a "new" (rebuilt) alternator fail withing 50 miles of driving... But your recent intake replacement invites the possibility of a pinched/shorted/cut wire. And the way that the gauge cluster was acting up like that suggests that the problem may not even be under the hood...

You said that the battery lamp comes on and off. Was it ON when you tested alternator output? What about the dash gauge? Does it dip at all when the battery lamp comes on? Is there any pattern to when the battery lamp illuminates, like going over bumps or anything?

no real rhyme or reason as to when the battery light comes on. it'll come on after about ~3 minutes at idle and likewise no real give away as to when it'll go off. the dash gauge doesn't change when the light actually comes on but when the dash goes dim and all my warning lights come on right before the engine dies, the volt gauge will dip all the way down but thats the only time it will.
the only thing that changed before and after the intake manifold install was that now the car will actually die out. i guess the next step is to read the voltages when the light is actually on

could be that the "new" refurbed alt is bad too but it puts out over 14 volts idle? ill find out if a warranty replacement is an option.
i know next to nothing automobile electronics guys lol
thanks for the ideas tho.

Take it to an Auto Electric shop, not a regular mechanic and have them find the problem (diagnose it). Then decide if you want them to fix it for you or if you want to do it yourself.

Electrical gremlins are a PITA and you sometimes need a scope and other diagnostic equipment to find the source of a problem or a much higher understanding of the cars electrical system to properly troubleshoot it. No shame in knowing your limitations. I hate electrical stuff. And the money you spend on a one time proper diagnosis will save you a **** ton of frustration, time and possibly more money if/when you start throwing parts at it.

And btw, if the battery light if flashing when you're driving or flickers, it's usually an alternator. My old 2000 V6 had a failing alt that was fine around town but, on the freeway under heavy load and WOT the light would flicker. It would progressivly get worse and a bench test was pointless (always tested fine which makes sense because it was much lower RPM and less load).

Finally took it to the dealer (this was back in 2005) and let them diagnose it. I had just moved here and didn't know where good shops were at. Bad alt. They showed me their test print out which not only tested at idle and regular RPM's but loaded the charging system like it was running WOT under a heavy load. The drop in performance was like a cliff on their graph.... thus the light flickering.

problem solved y'all. warrantied the alt for another remaned rotorcraft unit. been driving it for about a week w/ no light on.

And the light doesn't come on any more? I"ve had the light come on and off for a few years now. I had the alternator checked out last summer and I was told everything was good.

just wanted to put this out there, i bought a cheap alt from ebay seller one time and had this issue, just cheap parts used in them beware

part of me still thinks its too good to be true that it was just a chummy alt, but yea...shes fixed lol. light hasn't come on at all. picked up both alt's from rockauto.