I have a 1992 f150, I have never had a problem with it charging, then one day it just died and the battery was dead. a guy gave me a jump and I made it home. I had the battery and alternator checked and they both showed good. Then I noticed that sometimes the battery light would be off and the charging guage was fine. I drove it to town and all was fine, All I did was turn it off to go eat, when I came back and started it the light was on again and guage shows discharge. The I noticed when I turned on my left turn signal, the battery light flickered a bit then went out and guages showed charge again. I already replaced the alt plug that the truck is known to have problems with. but it still does it. I started it at walmart and the light was on, I turned on the left turn signal and after a minute the light went out and charged fine. I gave it some gas (in park) and the light came back on. I turned on the left signal again and the light went out. the other day, I would start it and the light may be on and I turned it back off and restarted and all was fine. I did the same thig several times but then after a bit when I started it, the light was back on. It;s driving me nuts because I never know if I should trust it or not. I also popped the hood while it was running with the light on and moved wires etc to see if I might find a bad wire, but nothing I did made it go off. But the after I drove about 10 miles, I had to turn on my left turn signal and the batt light flickered a bit then went off and started charging again. I drove it after that and turned it off several times and the batt light stayed out and charged, just never know when it will be on if you turn the truck off and restart. Any help would be much appreciated.
thanks, rudedawg

 

Welcome to the forum!!

Take a volt meter and check the voltage between the negative and positive terminals of the battery. Should see at least 12.4 volts or so with the engine not running-and no electrical accessories on-ie: the interior lights off and hood light pulled out .

Start the engine and then do the same-should see at least 13volts with the engine running.

Keep the engine running and then turn on your headlights and place the blower motor on high and turn on all accessories. Should see at least 13 or more volts still across the battery terminals.

If the voltage is low with the engine off -but is normal when the engine is running-I would suspect a bad battery. Have the battery load tested-Sears can do this.

If the voltage isn't at 13 or above when the engine is running-I would suspect the alternator or it's wiring.

 

Thanks for the quick responce. I tested it when the truck was not charging, the battery has 12.5 but then when I started it, it only showed 11 something, it was discharging while running. but when the light is out and the guage shows good amp charge (as it normally was before this) It charges fine with the headlights, radio heater etc all running. It just sometimes charges and sometimes dont, and I never know when I turn the key, which one it will be, even if it was fine when I turned it off, it may be not charging when I start it back up again.
thanks again, rudedawg

 

Sounds like a bad alternator/voltage regulator .

Is the alternator original? How many miles on the alternator?? How old is the battery??

Unless the battery is brand new-I would have it load tested. And then have them check the output of the alternator.

I also have a 92 F150 and I replaced the fire prone original 2G alternator with a 3G 95 AMP alternator that doesnt have a "burn down the truck" connector that the original 75AMP alternator has.

Whats the weather doing up there in Indiana? We got snow here in Denver and it is 10 degrees!

 

your temps are a bit lower than ours right now, but its pretty darn cold here too. I dont know for sure how many miles on the alt. The guy I bought it from his widow, I do remember seeing in his records that he replaced the alt. The battery is about 4 years old. I took both of them to advanced auto parts and autozone to be checked, they both said the battery was good but needed charged and the alt showed ok. Im not sure if I have an external voltage regulator or if it is built in to my alt. I just dont understand why it will work fine sometimes and just turning it off can make it stop charging when restarted or visa versa.
thanks and try to keep warm, Im sure we will have snow soon enough lol.
thanks again, rudedawg
p.s. love this forum, glad I found it when searching for answers to this problem

 

The light green and red wire is hot in run and provides power to excite the alternator into charging.
If you have an intermittent break or short in this wire it might cause the symptoms you describe.
You should also check the fuse for this circuit.

http://www.fordfuelinjection.com/pub...ALT_wiring.gif

 

When the battery was checked-was it "load tested"?? Charge up the battery and then have it load tested. Four years for a battery in cold climate is old age.

 

I charged the batter complrtley the night before, took it to autozone and advanced. they both said "battery good but needs charged i dont see how it needd charged the next morn when it wasnt attached to a vehical at all. but the batt stays charged as long as the charging light and meter show charge.' thanks again for all the help you all have offred a newbie, most forum wont help a newbie as much as a senior member, you guys are great and appreciated
rudedawg

 

Replace the battery, if it says it needs a charge after a full night of charging, then it is not holding a full charge. Replace the batt, MAKE SURE YOU CLEAN AND TIGHTEN THE CABLE ENDS. A bad battery will cause the alt to over work and wear out early (I almost ALWAYS sell a battery when replacing the alt, just to be safe)
After replacing the battery, keep a VOM handy and as soon as the light comes on pull over and check the voltage at the battery (DO NOT TURN THE TRUCK OFF), should be atleast 13 volts, 13.5 is better.
If it shows in the low 13 range it may still be weak, if it shows under 13 it is junk. More than likely if it still does it with a new battery then you have an intermittent Voltage regulator problem and that is in the alt.

 

Sometimes the light will come on if it is over charging more than 14.5 volts could be considered overcharging, this will wear out the battery faster than usual.

 

thanks for all the help, i will try these things when santa has a bit of spare change for a batt and alt lol