Electrical issue
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4wd Low
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Electrical issue
Howdy Yall,
I ran into an issue recently with my 73 Ford. It completely died in the neighborhood a couple days ago. Got it back in the garage and did some troubleshooting which led me to believe the alternator was bad. Got a new one, swapped it out and recharged the battery. Initially, the truck wouldn't start. Not a bit of power. I checked all my connections and the were good. I traced it back to corroded battery terminals. Once I got all those cleaned up the truck fired right up... except now the alt light is constantly on in the dash. Can't figure out why. I also checked the voltage and it read 12.75 v at the battery and at the back of the alternator. Any help is appreciated. Thanks!
I ran into an issue recently with my 73 Ford. It completely died in the neighborhood a couple days ago. Got it back in the garage and did some troubleshooting which led me to believe the alternator was bad. Got a new one, swapped it out and recharged the battery. Initially, the truck wouldn't start. Not a bit of power. I checked all my connections and the were good. I traced it back to corroded battery terminals. Once I got all those cleaned up the truck fired right up... except now the alt light is constantly on in the dash. Can't figure out why. I also checked the voltage and it read 12.75 v at the battery and at the back of the alternator. Any help is appreciated. Thanks!
Last edited by Gunslinger44; Oct 15, 2023 at 04:36 AM. Reason: forgot some info
Moderator & parts slinger
Joined: Feb 2007
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From: S/W Missouri, Polk county
Check out this thread...FMC400 is the man on elec systems. https://www.ford-trucks.com/forums/1...-stays-on.html
"If you turn the truck OFF, unplug the regulator, then turn the key to RUN, does the ALT light stay on? If YES, there's a short in the wiring upstream of the regulator. If NO, there is a stuck ground in the regulator or the regulator is not getting a signal from the alternator stator.
The regulator is supposed to ground out the 'I' terminal of the regulator until it senses voltage at the alternator stator. The 'I' terminal can get stuck grounded (or close to ground) while still controlling the alternator output enough to let the battery charge. It's also possible for the regulator to still let the alternator produce current without having gotten a stator signal, but the output will not be regulated properly. Since you're seeing a healthy 13.5 volts, that implies the first - bad regulator (just not all the way bad). It wouldn't hurt to check all the wiring in between just for good measure.
The dim test light doesn't tell you much; it makes sense that it lights up a little bit if the ALT light is on. The reason for this is because there is impedance in between the 'I' terminal of the regulator and ground when it's closing the ALT light circuit, so you'll pick up a voltage here which will light up the test light some."
"If you turn the truck OFF, unplug the regulator, then turn the key to RUN, does the ALT light stay on? If YES, there's a short in the wiring upstream of the regulator. If NO, there is a stuck ground in the regulator or the regulator is not getting a signal from the alternator stator.
The regulator is supposed to ground out the 'I' terminal of the regulator until it senses voltage at the alternator stator. The 'I' terminal can get stuck grounded (or close to ground) while still controlling the alternator output enough to let the battery charge. It's also possible for the regulator to still let the alternator produce current without having gotten a stator signal, but the output will not be regulated properly. Since you're seeing a healthy 13.5 volts, that implies the first - bad regulator (just not all the way bad). It wouldn't hurt to check all the wiring in between just for good measure.
The dim test light doesn't tell you much; it makes sense that it lights up a little bit if the ALT light is on. The reason for this is because there is impedance in between the 'I' terminal of the regulator and ground when it's closing the ALT light circuit, so you'll pick up a voltage here which will light up the test light some."
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