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77 F150, 300 6-cyl, flatbed (originally a styleside)
I'm the second owner and am about 5k from reaching half a million miles. I LOVE this truck!
Anyway, my battery gave up the ghost this month, no problem it was old anyway. I replaced it and the new one promptly died in less than 24 hours. Naturally the first thing that came to mind was an ignition-off draw.
With a digital multimeter in series between the disconnected ground cable and the battery post, I was seeing 3 amps. Holy Cow. Pulled every last fuse, one-by-one, still three amps. Turns out I had the multimeter lead in the wrong port. OK, just me not paying attention. Now I'm showing 16 milliamps, well in the normal range. Then on to check the charging system for good measure.
I figure my battery was getting boiled dry by overcharging. The question....is this generally a stuck voltage regulator that is full-fielding my alternator? That seems like an awful lot of voltage from a normal alternator. Doesn't a full-fielded alternator only put out maybe 15-15.5 volts at best?
Thanks,
Mike
Last edited by Michael Charlson; Mar 23, 2017 at 03:07 PM.
Reason: Grammar
I am far from an expert but have always heard 13.5-14.5V as a max. 17.5 sounds awfully stout to me. I would lean toward the regulator being bad
(obviously the alternator is doing its thing, and the regulator is supposed to give you steady output current and is doing so at the wrong voltage) but I will freely admit that my knowledge is at best incomplete. Let's just say that my total experience has been with too little juice, not too much!
yeah that's too much. either the regulator or bad wiring, bad connection between regulator and alt. maybe a bad ground strap. something is making the alt. think the battery needs charge
Last edited by nakedpancakes; Mar 24, 2017 at 11:01 AM.
Reason: extra thought
I thought finding what the full field voltage would be an easy thing but am proven wrong. I'm thinking I've heard 18 volts but could be making it up at this point, my high school vocational automotive class was 38 years ago.
I do know that some Ford alternators put out 110 volts for the windshield defroster but they were on the big sedans.
Thanks for the input guys.
Having spent decades as a Ford service tech, I generally despise shade-tree hacks who only throw parts (and money) at a problem until it is solved. I'm WAY too OCD to do that. I want to know precisely what the problem is before I spend a dime.
In this case, I believe I'll break my own rule and throw $15 bucks at it in the form of a voltage regulator.
I figure my time (and the aggravation) is worth more than that.
I fabricated my own charging system harness about 20 years ago and it's worked perfectly. I didn't like the little weenie 18ga. wiring and especially the fusible link. (installed an accessible in-line fuse holder as well)
I was concerned about the output voltage I was seeing since I honestly hadn't seen that before...ever. I didn't think that little alternator had the giddyup for that much voltage...especially since the engine was only at a high idle when I read the 17.5.
Thanks for the input guys.
Having spent decades as a Ford service tech, I generally despise shade-tree hacks who only throw parts (and money) at a problem until it is solved. I'm WAY too OCD to do that. I want to know precisely what the problem is before I spend a dime.
In this case, I believe I'll break my own rule and throw $15 bucks at it in the form of a voltage regulator.
I figure my time (and the aggravation) is worth more than that.
I fabricated my own charging system harness about 20 years ago and it's worked perfectly. I didn't like the little weenie 18ga. wiring and especially the fusible link. (installed an accessible in-line fuse holder as well)
I was concerned about the output voltage I was seeing since I honestly hadn't seen that before...ever. I didn't think that little alternator had the giddyup for that much voltage...especially since the engine was only at a high idle when I read the 17.5.
Again, thanks!
Mike
Hey Mike, I'm experiencing the same problem. Did the voltage regulator fix it?
If I'm saying things that you already know, no offense meant.
#1 Make sure your battery is disconnected first. The ground cable is good enough.
#2 Most importantly, grab a wire brush or sandpaper and make sure the chassis is down to bare metal where the two screws that attach the regulator are.
Good luck, you got this 👍
P.S. Since I don't know what problem your having, if this doesn't correct it, I'd be happy to answer any questions you may have.
If I'm saying things that you already know, no offense meant.
#1 Make sure your battery is disconnected first. The ground cable is good enough.
#2 Most importantly, grab a wire brush or sandpaper and make sure the chassis is down to bare metal where the two screws that attach the regulator are.
Good luck, you got this 👍
P.S. Since I don't know what problem your having, if this doesn't correct it, I'd be happy to answer any questions you may have.
mostly stuff I'm aware of, but never hurts to be reminded. I am not a mechanic by trade, just by hobby. Thank you! One nice part: to get at the voltage regulator I have to remove the battery, so I'm sure to have it disconnected!
If I'm saying things that you already know, no offense meant.
#1 Make sure your battery is disconnected first. The ground cable is good enough.
#2 Most importantly, grab a wire brush or sandpaper and make sure the chassis is down to bare metal where the two screws that attach the regulator are.
Good luck, you got this 👍
P.S. Since I don't know what problem your having, if this doesn't correct it, I'd be happy to answer any questions you may have.
Hey dude just wanted to come back here and say thank you for the help, after installing the new voltage regulator I'm seeing correct numbers all around!! Appreciate the support!
And just to finalize one bit of info, although anyone reading this thread probably realizes it already, that 17+ volts is quite normal for full-fielding or a failed regulator allowing an over-charge situation.
Seen it many times over the years and it always peaked at just above 17v on the ones I saw.
Thank you! One nice part: to get at the voltage regulator I have to remove the battery, so I'm sure to have it disconnected! 
