Battery Light
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Battery Light
I have a 1988 F-150 4x4. The battery light has started blinking on and off. There is no pattern to this. Sometimes it will blink a few times or may stay on for a while and then off for a while. The gage showes the battery to have about 12 volts and when I start the truck it goes up to about 14.5 volts. No problems with starting the truck. What could be causing the light to blink. 
Posting Guru
Joined: Dec 2001
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From: Southeast FLA
Battery Light
First and foremost, I'd suggest you use a digital voltmeter to measure the system at the battery.
Without the truck running (after it's been sitting awhile), does the battery read less than 12.6 volts?
Holding the voltmeter's terminals to the battery, when someone else starts the truck, does the voltage at the battery dip down below 10 volts?
Running, at idle, the voltage is ___?
ALso i've seen shorts to the main lead going to the alternator cause this, but check the above first.
Without the truck running (after it's been sitting awhile), does the battery read less than 12.6 volts?
Holding the voltmeter's terminals to the battery, when someone else starts the truck, does the voltage at the battery dip down below 10 volts?
Running, at idle, the voltage is ___?
ALso i've seen shorts to the main lead going to the alternator cause this, but check the above first.
Senior User
Joined: Feb 2002
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Battery Light
try putting a load tester on the battery while the truck is off. the tester will tell you if the batery has a bad cell. also, do the same withthe truck runing to see if the voltage regulator is working. I have the same problem with my 89 f250, except it is with the check engine light. i put it on a scan tool, and no codes came up. i traced it to a bad gas cap.
Posting Guru
Joined: Dec 2001
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From: Southeast FLA
Battery Light
That number during start-up would indicate to me that it might be losing some of it's cranking strength... but I doubt it is the problem.
lessee here... do ya have corrosion on either terminal? (clean 'em off)
But I think I'd start looking at all the wires going to and from the alternator, following them out with your hands to make sure one isn't starting to rub through and short out. The last time I saw the symptom with a Bronco II the main red wire going to the alternator had worn itself apart, yet welded itself to a support-bracket at both ends to keep the electrical flow going most of the time. Finally a wire was just breaking off from it's poor weld and it wasn't charging right, plus the light was coming on.
But this really could be a myriad of things. Find one aspect you want to investigate and then investigate it fully to rule it out. You didn't say how many miles were on the truck, but maybe the alternator really is starting to go on it?
lessee here... do ya have corrosion on either terminal? (clean 'em off)
But I think I'd start looking at all the wires going to and from the alternator, following them out with your hands to make sure one isn't starting to rub through and short out. The last time I saw the symptom with a Bronco II the main red wire going to the alternator had worn itself apart, yet welded itself to a support-bracket at both ends to keep the electrical flow going most of the time. Finally a wire was just breaking off from it's poor weld and it wasn't charging right, plus the light was coming on.
But this really could be a myriad of things. Find one aspect you want to investigate and then investigate it fully to rule it out. You didn't say how many miles were on the truck, but maybe the alternator really is starting to go on it?
Posting Guru
Joined: Jan 2001
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From: Rural Florida Panhandle
Battery Light
I had to replace the alternator on my 88 F150 5.0L because the heater hose connection was loose enough to let it drip coolant onto the alternator. Caused it to short out.
Sounds like your problem is intermittent. If you could check your battery voltage while the battery light is on, it would be more useful. Short of having that opportunity, I would check the wiring to the alt very closely, and for good measure, buy a new set of brushes and install. Could be you have worn brushes that are sometimes not making good contact.
Winford
Sounds like your problem is intermittent. If you could check your battery voltage while the battery light is on, it would be more useful. Short of having that opportunity, I would check the wiring to the alt very closely, and for good measure, buy a new set of brushes and install. Could be you have worn brushes that are sometimes not making good contact.
Winford
Senior User
Joined: Jan 2002
Posts: 185
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From: Central Florida, USA
Battery Light
One of the reasons that light will illuminate is to indicate when the battery alone is supplying power to the vehicle, which means the alternator is not producing a voltage equal to or grater than the battery charge. In the old generator days that light used to come on while idling or at lower RPMs when lights, fans and wipers were all on at the same time. Since alternators have replaced generators and higher current is available at low RPMs we usually only see this light when the key is in RUN and the engine is off, or when there is an alternator/chargeing system problem.
Check the connections and wires on the alternator. Most auto parts places will test your alternator for you (but mine likes me to have the unit off the car and for me to take it inside). Sounds like your battery is okay but as the other posters suggest make sure all the cable connections are clean and no chaffing is present. Hope this helps.
Check the connections and wires on the alternator. Most auto parts places will test your alternator for you (but mine likes me to have the unit off the car and for me to take it inside). Sounds like your battery is okay but as the other posters suggest make sure all the cable connections are clean and no chaffing is present. Hope this helps.
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Postmaster
Joined: Jul 1999
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Battery Light
The rectifier & regulator connections on those models of Ford trucks have been fire hazards over the yrs . The connecters work loose over time , excessive heat builds up from the loose connection , the wiring harness melts & can eventually cause a fire . It sounds like the alternator is dying . If you find thats the problem make sure you replace both the rectifier & regulator connecters . One sure way to tell is remove , esp the rectifer connecter , if you see any signs of melting , replace it today . Id opt for the Ford alternator , they also have the connecters . Stay away from the alternators from places like Autozone regardless of what kind of warranty it has . Trust me , Youll be replacing it on a regular basis . The Ford ones have a 1 Yr warranty .
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