Charge light issue

[jadack]

My 2005 Sport Trac just began illuminating the charge light while driving. Goes out at low speeds and at idle. Holding the engine at 2-3000 RPM doesn't cuase the light to come on!! Just seems to be road speed!! Weird! I find that driving above 30MPH will cause it to come on and at that speed and cruising the RPM are very low. Below 30 or so it stays out even if I have it in 1st gear and the RPM is high. ???
Seems to be charging as I have no battery issues. My voltmeter just failed so I can't actually check the voltage.

Road speed is what sets it on??
Any Ideas??
Jennifer

 

[01STrunner]

I think it's still RPM driven as the shift points are right around those speeds. Your best bet will be to swing by any auto parts store (Advance, AutoZone, Oreilley's, etc) and ask them to do a battery and alternator test. They'll do it for free and will be able to tell you if its a bad cell in the battery or your alternator.