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What do you mean won't stay charged ? Battery dies while driving , dies over night ? Is the battery symbol lit on the dash , check charging system message on driver info center ? If it drains over night there is a parasitic draw on the electrical system ! If while driving the battery goes dead it's not charging , with a new alternator the problem is in the electrical circuitry . Blown fusible link or fuse . This charging system is controlled by the PCM - engine computer , the heavier gage wire on the back of the alternator should have battery voltage , if not blown fusible link near the battery . The connector with three wires ,one should have B+ voltage , the other two come from the PCM .
Have you tried adjusted the dimmer switch??Some other things to check are your grounds and the charging system.The ground between the engine block and firewall/chassis is the ground for the interior & exterior lights so make sure its tight and corrosion free.
The next thing you should do is conduct a full charging system test. Here’s how to do your own.
Connect a digital volt meter to the battery terminals. A fully charged battery should read about 12.7-volts. Start the engine. The reading should jump to around 13.5 volts. Leave the engine running and turn the blower motor to HIGH. The reading should dip down and then rebound back to 13.5 or more volts. Leave the blower on and turn on the headlights. It’ll dip again and rebound. Then turn on the rear defroster grid. Next, sit and watch the meter for about 10 minutes with the engine running and all those accessories on full blast. If the voltage stays the same at 13.5 or higher, the charging system is fine. A weak alternator will start pulling the voltage down in small increments because it can’t keep up with the electrical drain.
You have a short somewhere in electrical system of truck that is slowly draining battery. When battery is too low, cranking speed and voltage is too low to operate electrical system to allow fuel etc to start truck. First make sure dome light is not staying on after you close door. Sometimes a kneecap hits the dash switch that turns on domelight. Second make sure battery is FULLY charged. Have auto store check battery to see if it is fully charging. At same time they will check to see if alternator is not malfunctioning and charging correct amount. Replace as needed. If all checks out OK...Third, get an amp meter, remove negative battery cable. Attach one probe to the negative cable and other to negative post on Battery. Turn amp meter on. It should read zero. If reads anything it is showing you have short in system. With meter hooked up this way(I use radiator clamps to secure probes to post and cable) Start pulling fuses first, one at a time, then relays in fuse box to until meter goes to zero. When goes to zero you have found the circuit. Look at fuse box picture in owners manual that came with truck. Replace relay or relay connected to the circuit shown in manual. For instance if fuse you pulled to make it go to zero...says it is for wipers and windows...look at manual diagram and locate and replace relay for wiper or windows one at a time, then check amp meter to see if battery drain continues...If you can't locate source of problem you have at least identified circuit. You can get all data schematics at library from ALLDATA free....then try to track down further...if not able to do yourself take to GOOD auto shop that does electrical work. OR.....buy at hardware, auto parts store or Wal Mart....Red wire at least 6ft long. one Toggle switch, get inline fuse connector and a matching fuse that matches the fuse you pulled out that makes amp meter go to zero( If 5 amp, get tubular 5 amp fuse for inline connector)...buy electrical wire connectors kit. Make two 3 ft long wires. Put connector onto both wires and screw tight onto toggle switch. Now cut one wire in half and splice inline fuse onto that wire with connectors. Next make a one prong connector for each end of wire. Carefully make it so you can plug one connector of wire into the left side of where fuse used to plug into fuse box. Then plug in other wire into right side of where fuse use to connect when plugged into fuse box. use electrical tape if need be so they cannot short across these two wires. Check with amp meter on neg cable and negative batt post to see if meter shows drain. If shows drain... simply switch toggle switch off. Meter should be at zero with toggle switch one way, then shows drain with other. Secure wires with plastic tie straps electrical tap, and duct tape the toggle switch to lower dash board area you can reach while driving. If your wipers or windows etc, aren't working with switch shutting off drain, simply turn on when needed and shut off when you park truck. Recheck with amp meter again when all secure...Good luck all!
Is this E-150 econoline?
Engine running, take reading at generator bat terminal, what is it? The basics, take reading across battery terminals, everything off. Take second reading at bat terminals, engine running. The second reading should be higher than the first if charging system is working. Was the charging system checked on the vehicle when the generator was checked out?
There could be a wiring circuit problem? The bat terminal at generator is hot all the time, engine running or off.
check all battey connections and system grounds. Check that the battery has 12v and holds properly when load tested. To check charging system, don't disconnect any battery leads...put a volt meter across the battery. when running, you should have at least 12.9v and volts should not drop. (usual reading is generally at or near 13) at idle with all accessories on voltage should be close to that as well. voltage should not exceed 14.Also make sure that drive belt is not slipping.
That sounds like normal operation...check your electrical system with a volt meter,check battery voltage with engine off...should be minimum 12.4 volts,i like to see 12.6 or higher at rest.Then check with engine running,as the alternator is charging or should be,and the voltage reading should be at least 13.5 up to 14.5 volts.Scan the vehicle for trouble codes,if none present,then the Check Engine light should be off.