battery light

[superdub01]

ok, i have a battery light constantly illuminated on the cluster. i have a new (4 weeks old) alternator, my belt is not slipping(its brand new). i took the truck to the parts store and had both batteries, and the alternator statically and load tested, with all the tests passing with flying colors. i also tried resetting the computer by disconnecting the batteries for 30 min. i have been driving the truck daily for about two weeks now with no symptoms other than that annoying light because i need it to get to work. just waiting for it to strand me. any ideas???

 

[arrowstrap]

i had the same issue exactly word for word so i took the new alternator out and had it bench tested. it passed as a good working unit, so i reinstalled it on the truck and the light has yet to come on again. i do not know what was loose but it seems to be tight now. it has been 4 weeks and still no light.

hope this helps.

 

[superdub01]

so possibly it is an alternator case to engine grounding problem? thats my only guess?!?! but why would that cause a warning light, even though the batteries are recieving, and delivering full charge even after prolonged use? is there a relay somewhere that is sending a false low/high signal? does anybody know where the sensor that sends the battery light is located so i can inspect the connection?

 

[Bad Night]

Sounds like the wire going to the gauge / idiot light isn't making good contact . Unplug it at the alternator and plug it back in . Maybe a little dielectric grease .

 

[JLDickmon]

the light works by Law of Opposing Voltages.
You have the battery on one side, and the alternator on the other both applying voltage to the lamp.. if it looses voltage source from either side, it becomes a ground path and the light illiminates.
That's the ONLY way these work and have ever worked.

So you either have a bunk alternator (bad diode, etc) or a wire chafed to ground somewhere.

 

[bigrigr]

X2!

 

[architect-builder]

Fairly cheap way to tell is just what I went through. When I lost my first set of batteries and alternator, my idot light never came on once.

Recently, my light kept comming on, then going off, coming on, etc.... had it tested, everthing seemed to test fine, then they tested the alternator with a older, non digital testor, it showed that the diodes were going bad. I installed a actual issopro volt meter, and it showed. Everthing seemingly normal, 13.5 to 14 , when the light would come on, 11.5 to 12, got worse as the engine got warmer.

My Guess, have someone test it with a non-digital testor, sometimes the oldtime stuff works better. Your "new" alternator could also be bad. My understanding is that our small case alternators are prone to failure on the bridge rectifier. I replaced mine with a High Output Large Case alternator, (I think they changed in 1999 from the large case to small case in d fords).

Barrett

 

[DaveBen]

Good information Barrett. Who would have thought that our old ways are still valid. Yea!!!!

Dave

 

[bigrigr]

Like JL said, something has to be shorting it to ground in the system, diodes can do this in the alt itself. It used to be very common, hence the old style tester working to detect this better?jmo

 

[ghoff]

do you have a single, or dual alternators? Is there batt. voltage at the big terminal on back of alternator? (key off, engine off) There is a fusable link on this wire, typicaly at starter relay that can go bad. Key on, engine off, is there 12 or more volts to one of the small wires at the alt.? Typicaly the PCM will turn on the batt. indicator light when a fault is detected.