my 98 f150 4.6 84k miles. battery light flash's on at up to 5000 rpm's +. just started doing this. do i need a new battery? it's the original battery. it only does this when i gun it up to high rpms.

i want to buy a tonneau cover (glasstite) does any one have this one? let me know what you think about it, then i want to add a remote release to it. www.glasstite.com $ 759.00 w/ headliner, painted to match. check out my truck photos under (divewithtom)
getting rid of the leer canopy. (very heavy)

 

Well it sounds like its your voltage regulator, if its internal then its in the alternator, if its external you can change it... The only way to find out is to put a voltmeter on the battery then have someone take the rpms up to 5000 then monitor what volts do the whole time if above 15 your voltage regulator is shot, if its below 12 then I would say your alternator, if its an internal regulator than you have to replace the alternator anyway...

 

More than likely your alternator is starting to fail. Mine started to do the same thing, not at redline but anything over 2500 rpm. If you do it at night, do you notice that the headlights dim? That's what mine did. I bought a replacement and installed it myself in about an hour. It's been fine ever since. Apparently the slip ring that transfer voltage to/from the windings starts to wear and vibrate at higher rpm's. this causes a loss of contact and no voltage output.

Here's a funny side to this story. My wife was using my truck and told me "your battery light came on when I was accelerating". I had not noticed this before and did not for another several months so I thought she must have been seeing things. I don't know how high she was revving the engine (manual trans) but it must have been way up there.

GlennMc.

 

My ranger did this. Started coming on at higher rpms with headlights dimming like glenns. Over time the point at which it turned on came with lower and lower rpm's. Eventually one day I could only go about 45 mph without it coming on. Then, it started dropping real quick and i had only about a mile i could go before i was running off battery. It looked like warn brushes once I openned it up. Got a replacement and it did the same thing after about a 2 weeks. Took that one in to test and they said the diode was failing. Warrentied the replacement and been running fine for a year.

 

my vote goes to alternator too. You can find em decently priced on ebay most of the time.

 

its the volatage regulator bulit in the alternator

thanks again

 

Glad to hear it.

 

same problem here. battery light came on yesterday when accelerating. 81K miles on truck. today battery light is on all the time. checked battery voltage at idle and while reving the motor. voltage at battery was constant at 12.36V, no fluctuations.

Any thoughts on why the battery light is on would be greatly appreciated.

Mike

 

sounds like alternator, I would keep an eye on it. I've had it once where my truck ran for about 3 days before it finally died.

 

12.36 voltage at battery with the engine running would sure make me go get an alternator.

tom