How can you tell if alternater is going bad - 1999 Ford Expedition

Was the alternator bad or going bad. Changing that won't change it starting. Just charging to keep running. As I tell others you need 3 things to make it start and run. Good battery for the starter. Fuel and spark. Test for gas and spark are needed to know which is not working. Did you run it out of gas would be my first guess

The voltage regulater mybe bad ! It maybe inside the alternater! So you may need a new alternater! Take it to auto zone and they Will check it!

the alternator doesn't start to work til the engine is running if the battery has tested good then use jumper cables from the battery to the block and the other from the battery to the starter this will tell you if the cables are bad if still cranks hard then the starter might be drawing to many amps

Tall tell sign that ur alternater is bad. Mine is doing the same getting it fixed tomorrow! These things happen just get a new or refurbished one. Problem solved!

The alternater has a regulator that is bad replace it and your good to go.

If the belt is still on and properly tensioned, it usually means a bad alternater. A bad battery is also possible, At many shops they will test this for free if you are going to have them do the work. If you want to do the work yourself, tell them up front and there will probably be a modest charge for diagnosis.

Dead battery.....bad alternater.....bad fan belt.....bad starter

If you lights and radio work, it probally isn't the battery or alternater

If the alternater light has come on in the car that means that the alternater is bad and you need to replace. You can also have it checked at your local auto parts store if you would like.

Good luck

Check wiring on alternator and battery. Also be sure that there are plenty of ground straps. there should be one from battery to body and body to motor. Without enough ground this could also cause your problem.

First tell me why you don't think it's charging.
Because of the voltage reading you are getting at the battery terminals? The range you want is between 13.6v to 14.2v. The higher the voltage the lower the amps. and true the other way, the lower the voltage the higher the amps. If you get a reading of 13.6v or lower, the alt is nearing or at max output. An alt can only run at maximum for around fifteen minutes and it will start slinging solder from overheating. It's a good indication the battery is either totally dead or junk. Charging above 14.2 the alternater is running wide open and is only putting out high volts which will cause the battery to boil , in turn destroying it. This is a bad alternater. All alternaters have integrated voltage regulater with the exception of ver few of the earlier ones. You cannot test an alternater by removing a battery cable to see if the engine keeps running without taking great risk of damaging the alt, regulator. So tell me why you feel it isn't charging. Remember an alt is not made to charge dead batteries. Their sole function is to maintain the battery charge. Without a battery, the alt won't last 10 seconds.
Hope to hear from you and good luck.