Need Electrical Help
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Need Electrical Help
Hey guys. I have a 1978 F100 that in the past week I have put a new starter, new battery, new alternator, new solenoid, and new voltage regulator on. It had been giving me electrical problems before but I just got it running after it sat for a a little over a year. Since putting the new stuff on I have had to replace the alternator this morning because the one I had put on from AutoZone was bad. I'm not sure if it was bad from the get go or went bad once on my truck but for some reason it wasn't charging the battery and now the new alternator isn't charging it either because it died on me (I think died due to fuel pump issues) but wouldn't start and battery is completely dead again after 100% charge this morning. Any idea what I am missing?
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Welcome to FTE Jeremy
Well, going only from the information provided, it sounds like you've got a defective battery, at minimum.
The only way dignostics can be done effectively though, especially over the internet, is one step at a time. And a fully charged, serviceable battery is the first thing to check for. It's important to do these tests in order and methodically, because while a defective alternator can ruin a good battery, a defective battery can also ruin a good alternator!
SO, the first question would have to be is A. How old is the battery, and B. what kind of charger specifically was used? Maybe you know all this stuff already, but since you are new here at FTE, nobody knows what your skill level or knowledge base is.
Well, going only from the information provided, it sounds like you've got a defective battery, at minimum.
The only way dignostics can be done effectively though, especially over the internet, is one step at a time. And a fully charged, serviceable battery is the first thing to check for. It's important to do these tests in order and methodically, because while a defective alternator can ruin a good battery, a defective battery can also ruin a good alternator!
SO, the first question would have to be is A. How old is the battery, and B. what kind of charger specifically was used? Maybe you know all this stuff already, but since you are new here at FTE, nobody knows what your skill level or knowledge base is.
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My knowledge is practically bumpkis. I inherited The truck a few years ago from my wife's grandfather. Both the battery and alternator were brand new last Sunday. Since then I have taken the battery back to AutoZone several times and whatever brand tester and charger they use there is what was used. I actually left it with them last night for them to charge and check and they say the battery is good just not getting charged from the alternator. Also of importance, after putting new alternator and charged battery on this morning had retested at different AutoZone after an hour of drive time. Battery tested at 96% but only 12.4 volts while running.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
OK, tracking now with where we're at. 12.4 volts is pretty low. It doesn't sound like they know how to charge a battery. Or, the alternator is toast. If you had your own charger, you wouldn't have to depend on them, just sayin'. If you want to do your own maintenance, it's a necessity.
Anyway make sure all the ground and battery connection cables at both ends are clean and tightened securely, same with alternator wires and connections. The belt needs to be tensioned properly too, if it's loose it will not charge the battery. If the battery cables starter and ground cables are original, these should be replaced.
When measuring for charging, do this right at the battery posts. Should see 13.8 to 14.3 volts at idle. Then, turn on all the headlights, radio, heater fan on HI, etc to test the alternator under load. Rev the motor up to a fast steady idle around 2000 RPM for several seconds. It should still measure in the high 13s or better. If not, the alternator is most likely defective.
Anyway make sure all the ground and battery connection cables at both ends are clean and tightened securely, same with alternator wires and connections. The belt needs to be tensioned properly too, if it's loose it will not charge the battery. If the battery cables starter and ground cables are original, these should be replaced.
When measuring for charging, do this right at the battery posts. Should see 13.8 to 14.3 volts at idle. Then, turn on all the headlights, radio, heater fan on HI, etc to test the alternator under load. Rev the motor up to a fast steady idle around 2000 RPM for several seconds. It should still measure in the high 13s or better. If not, the alternator is most likely defective.
Postmaster
Joined: Mar 2011
Posts: 2,698
Likes: 7
From: Taxachusetts
Agree with Tedster9 about cleaning up the basics...like a fully charged battery...clean and tight battery (or any electrical connections) connections, solenoid connections..make sure the solenoid is grounded to a clean piece of the fendewell - the mounting screws are the holdowns for the solenoid's ground.....clean and tight engine to cab grounds, etc.
Once that is a known, we can start troubleshooting other "knowns"....such as alternator AC ripple (will test the diodes), or full fielding the alternator - will test the alternator's output, or..not to spec output which would either confirm or deny regulator problems or alternator problems.
But first, clean up the basics as stated before.
Once that is a known, we can start troubleshooting other "knowns"....such as alternator AC ripple (will test the diodes), or full fielding the alternator - will test the alternator's output, or..not to spec output which would either confirm or deny regulator problems or alternator problems.
But first, clean up the basics as stated before.
More Turbo
Joined: Feb 2018
Posts: 710
Likes: 3
From: Oregon
Wait - you said you measured only 12.4 volts while running? That means your alternator ain't doing something it is supposed to.
And I wouldn't be surprised if you may have just killed the brand new battery cause it wasn't charging. A lead acid battery's life is greatly reduced when it goes under voltage. You should see almost 14 volts at the battery when the vehicle is idling.
And I wouldn't be surprised if you may have just killed the brand new battery cause it wasn't charging. A lead acid battery's life is greatly reduced when it goes under voltage. You should see almost 14 volts at the battery when the vehicle is idling.
Tuned
Joined: Jan 2016
Posts: 311
Likes: 35
OK, tracking now with where we're at. 12.4 volts is pretty low. It doesn't sound like they know how to charge a battery. Or, the alternator is toast. If you had your own charger, you wouldn't have to depend on them, just sayin'. If you want to do your own maintenance, it's a necessity.
Anyway make sure all the ground and battery connection cables at both ends are clean and tightened securely, same with alternator wires and connections. The belt needs to be tensioned properly too, if it's loose it will not charge the battery. If the battery cables starter and ground cables are original, these should be replaced.
When measuring for charging, do this right at the battery posts. Should see 13.8 to 14.3 volts at idle. Then, turn on all the headlights, radio, heater fan on HI, etc to test the alternator under load. Rev the motor up to a fast steady idle around 2000 RPM for several seconds. It should still measure in the high 13s or better. If not, the alternator is most likely defective.
Anyway make sure all the ground and battery connection cables at both ends are clean and tightened securely, same with alternator wires and connections. The belt needs to be tensioned properly too, if it's loose it will not charge the battery. If the battery cables starter and ground cables are original, these should be replaced.
When measuring for charging, do this right at the battery posts. Should see 13.8 to 14.3 volts at idle. Then, turn on all the headlights, radio, heater fan on HI, etc to test the alternator under load. Rev the motor up to a fast steady idle around 2000 RPM for several seconds. It should still measure in the high 13s or better. If not, the alternator is most likely defective.
Tip for getting that alternator belt nice and tight: use a pry-bar or something to push the alternator until the belt is tight (or have someone help you) while the bolt is tightened.
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Laughing Gas
Joined: Apr 2016
Posts: 858
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From: Buffalo NY
Check the connector at the regulator for corrosion or broken wires. New ones are available at NAPA .https://www.napaonline.com/en/p/ECHVRC428
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From: S/W Missouri, Polk county
I always have a new alternator or starter bench tested before I walk out the store. X2 on ck and clean all elec connections. New cable are not that much and then you take that possibility out of the equation.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
Originally Posted by Charles Howard
Is there a reliable way to test that the cables are doing their job well?
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