I was coming home from work and my lights dimmed so i thought it was my alt. so i took it off and had it tested, it was perfect. I then changed my battery because i thought it may have been bad. As soon as i turned the truck on i could watch the amps gauge drop until it was 0. Then the truck will start to sputter and spit i am assuming because the fuel pump doesnt have enough power..my truck is a 1998 f150, 5 speed, 4.2lt.
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Re: my battery drains almost instanly
You may need to have it test with a load, i.e. while still in truck. While there is no load it is possible for it to check out as good, but once it needs to "work" it will give out. The other option could be that there could possible be a wiring problem. The wire from the alternator is coroded or broken. Use a volt meter to check votage at the begining and end of each wire.
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Most likely a bad alternator..batt isnt gittn chargd. The diode is bad causing the alt to suck juice from batt. Also the main wire from battery to back of alternator I wud test first for wear. A bad one impedes chargn
The alternator may charge fine but could drain the battery through a bad diode,have you checked the alt for a bad diode?Disconnect the battery positive cable.Put a regular 12v test light between the battery positive post and the positive battery cable.If the test light is bright you do have a drain,if dim it is OK.A dim light may mean the drain is internal in the battery.If you do have a bright light remove a fuse ,one at a time from the fuse box until the light goes dim.Once dim you have identified the bad circuit.If removing all fuses do not dim the light,disconnect the alt charging wire at the alt,if that dims the light,then you do have a bad diode.DO NOT create a drain(bright light) when checking for the drain by turning on the key or opening a door/trunk etc.
Also,do an overnight battery check by disconnecting the battery overnight,if things are fine the next morning after the battery was disconnected then it is a drain in the vehicle,if the battery is dead even after being disconnected overnight,,then the battery is bad.
Disconnect battery from vehicle overnight to check for internal battery drain.......just take one of the cables off. If the battery is still up and starting the vehicle after being disconnected after a day or two......the drain IS in the vehicle and will have to be checked again. Do it yourself. Buy a cheap 12 volt test light. Place it between the cable you removed before. One end on the battery post and the other on the cable end. Now....with the key off...... If the light glows brightly....you have TOO MUCH drain. We want a dim glowing light. The dim light is just the memory circuits in the electronics and OK.
With the doors closed....take out one fuse at a time until the light glows dim.......the fuse that dims the light is the problem circuit. If no fuse dims the light...remove relays one at a time. Remember....some fuses and relays could be in the engine compartment and under the dash. If no relay dims the light disconnect ALL alternator wires. Remember....anything that uses power will make the light glow ....keep those doors closed (we do not want interior light drain affecting the test ) and if you have a under hood light check it first by removing the bulb. We do not want false readings.
Use a 12volt test light between the positive battery post and the positive cable with the positive cable disconnected from the battery. Keep key off. You will see the test light "light" with any drain.
Any drain showing a dim test light is..... OK Any drain showing a bright light is.....BAD
Disconnect items (fuses) one at a time and watch the light. Keep the doors closed....the inside dome light is a drain with the door open! After fuses are checked....disconnect the alt if needed and watch the light. Keep going until you get rid of the bright light.
FULLY CHARGE BATTERY BEFORE USING.If you dont you will burn out the alt. within minutes.
Does the new alt have all the same connections as old one?
After charging bat and installing new alt. typical battery load test and alt. output test should tell if there may be other problems.
Probably it is not just charging well.
Go to Autozone store and for free they will check the battery voltage and alternator current. Draining of battery during driving means the alternator not charging the battery back or alternator is not providing current which is less than car consumed and the additional current coming from battery. The common symptoms might be the dimming the lights, heater flow on idling or than rpm goes down.
Hope that helps
you should remove your alternator and take it into an auto parts store and they can test it for you.
this alt had an internal regulator which can be replaced easy.
your auto parts store will be able to full feld your alt to bypass the regulator. this is how you test it to see if the regulator is bad.
you didnt say how many miles are on this truck .
most of these ford alt will last 120,000 or more
on the back side of the alt you will see the replaceable regulator.