My 2003 ford expediton battery light came on so I changed the belt the belt tensioner the alterntor and the battery and when start up battery

Your belt is stretched and not charging the system or your tensioner is bad or both.Here's a link to it,the part is number one on the picture,also watch belt as it turns and rev up and see, Repair Guides Charging System Alternator AutoZone com

sound like alternator faulty.remove it let auto parts store person check it out.

Is the alternator putting out 14+ volts when it is running? If so is it a cheap alternator? The bearings might be bad. Could be water pump or anything the belt drives such as the A/C. Have the battery tested ASAP then the alternator.

voltage regulator?

Could be a wet or bad belt, belt tensioner or one of the other pulleys.

Try replacing your Belt tensioner and the Serpetine belt. When your A/C clutch cycles the tension changes and your belt is slipping on the Alternator pulley. The A/C compressor will turn off on heavy acceleration to boost speed.

This could explain the light coming on at certain speeds. The modern Alternators contain Voltage Regulators. The Regulator would be the only other part that could cause your problem. Since you replaced the Alternator, it would contain another Regulator.

Make sure the Battery cables are clean and tight. Put both the Tensioner and Belt on as a pair this time. This will insure the tightest fit possible.

As long as you put in a 12 Volt battery connected to the correct terminals, there is little you could do wrong with the battery.

I hope you are happy with my reply and Thank You for using Fixya!

sounds to me like you better find another dealer or possibly an auto electric dealer they should have done it right the first time

Either the fuse is bad, or the connection to fuse block is bad which is common, or lastly, a faulty ECM

The tension is set automatically with the belt tensioner. It looks like a pulley. You put a wrench or socket on the bolt in the center of the tensioner and apply pressure. It is spring loaded. As you apply the pressure it will release the tension on the belt for removal or installation.

replace the drive belt and have the alternator tested