Wierd issues: battery light comes on at 2500 RPM

emkorial · 04-09-2004

Wierd issue: 99 Mustang, V6, 77K miles

I was driving home from a vacation with the wife, highway driving, about 70 ish, and I notice the battery light is on. I drive that way for 2 hours till I get home.

Upon getting home, I drive a few other places that day, light stays on the whole time, however, no problems starting/radio & CD player work, no electrical problems at all.

I go to Lowes, and upon going back to my car, I notice my trunk wasn't latched all the way. I open it and close it all the way. To my surprise, when I start the car, battery light is off.

I go on for the next few days, everythings fine, ect.

I go down to AC for some poker lovin'. I notice that at high speeds, the light will start to flicker to life, and go on, then go off as I slow down. I do some testing, and realize that it starts to come on when the engine hits 2500-ish RPM. Above that RPM, it's on, below that RPM, it's off.

This whole time, I have no electrical problems or starting problems with my car.

What could this be? Any idea's?

vdog · 04-10-2004

have you went to a local parts store and had the alternater checked for free yet.....

I think "advanced auto parts" stores do it for free....

stangcrazy94 · 04-10-2004

uhh? no battery problems? it sounds like there could be a short somewhere...???...my battery light flickers when i stab the throttle pedal at idle but when i look at the gauge the voltage goes up! wierd huh?

Tominator · 04-10-2004

If all the connections are clean and tight, I'd guess the alternator has blown a diode. Usually there are two of them. If one goes the alternator will charge at a lower voltage. Then if your lights or blower are on they will drop the voltage below a certain level and trigger the idiot light.

Get the alternator checked.

emkorial · 04-15-2004

Seeing as I'm kinda broke, whats the worst case if I don't get it fixed?

stangcrazy94 · 04-16-2004

you could have a break down on the road if your alternator isn't charging your battery!

emkorial · 04-17-2004

Well, I've been keeping an eye on my voltage guage, and it;s heald steady at the exact same level as it aways has. If the alternator wasn;t charging the battering, wouldn;t the voltage drop?

Mana4Real · 04-17-2004

One: Stock guages suck...
Two: Alternators have 3 diodes
Three: It may not be undercharging at 2500, it may be overcharging. The "Voltage Regulator" might not be functioning very well. I would get the alternator checked. I would borrow a voltage gauge and check the voltage at the battery at idle and then again at let's say 3000 rpms...
Four: Overcharging is worse then undercharging, It can fry all the electronics in your car...
Five: Fix it...

I'm not trying to be a smart ass, just straight to the point