fordhippie

so heres the deal. i have a 95 f150 5.0 v8.
the other day, driving to work, the batt/charging light came on. after work, the truck started with no problem, the light didnt come on and the volt gauge was reading normal. about 20 minutes in to my 25-30 minute drive, the light came on dropped well below normal. well i made it home. a few hours later i went out to check things out. i tested the battery with my voltmeter and it was reading around 12.5. i started the truck and checked again and it read around 14.3. then with the lights on and heater on, it read around 14.
i let the truck run for about 20 minutes or so and the light comes on. so i check the volts again (lights and heater off) and this time it read just above 13. and i kept checking every few minutes and everytime i checked, the volts were dropping just a little at a time (13.1, 12.9, 12.6, 12.5, 12.3, etc.).
if i let the truck sit for awhile and go start it, it will show a normal volt reading until it runs for about 20 minutes, then the whole process of the light coming on and volts dropping starts all over again.
i have checked the battery posts, connections, and wires.
also, i noticed that about every 30 seconds or so you can see a small blue spark inside the alternator (rear) and a few times i have noticed the spark actually coming off the rear side of the alternator body.
any thoughts, ideas, suggestions would be greatly appreiciated.

broncojunkie

Check the plugs on your alternator and make sure they're not corroded. If they don't look nice and shiny, clean them up good and use some dielectric grease on the connection. If they look good and you're still having issues, I would pull the alternator. Take the voltage regulator off and inspect it. Clean it up if it doesn't look to hot. I wouldn't suggest replacing it. I think they're a little pricey and usually not worth replacing on an older alternator, since you never know how much longer your alternator will last. I always figured it's best just to change them out. I changed the vr on mine once and found out later that the bearings were bad. You can, however, replace the brushes in the alternator while it's out. Very easy and I think they're less than $5 at the parts store. After inspecting, cleaning, replacing whatever is bad, then you can take it to the parts store and let them bench test it. Or better yet, have them do it before and after you do your thing. If the alternator tests ok, see if they can hold a heat gun on the vr and re-test. Just explain to them what's going on. If you determine you need a new alternator, you might consider an upgrade.

fordhippie

ok thanks for the advice.
someone had told me that something in the alternator (not the regulator, but something else....a diode or something like that) has either gone bad or is going bad and its causing my problem. said that the alternator is still charging the battery but with the part thats gone bad, when the truck has ran for awhile and requiring power for brake lights, radio, turn signal, etc etc, its not letting the alternator put out enough juice to keep the charge up to par.
does that make sense or sound like it could be the problem?

techrep

iTrader: (1)

Replace the Alt...its going bad..

fltdriver

x2 on replacing, go with either a 90 or 130amp 3g alternator. I went with a 130 and couldn't be happier, $110 shipped from rockauto (TYC brand). I upgraded the alt>sol wire with a 4ga battery cable and 150amp breaker, took the original alt>sol wire and added it to the battery>bodyground as well as replacing both battery terminals and cleaning up connections/grounds. I can run an e-fan, all lights, stereo/subs, Max A/C on High, and run the wipers and nothing ever dims. I was on the fence about 90vs130 but so glad I went big, so much power left I just want to keep adding stuff.