voltage regulator blues
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Junior User
Joined: Jun 2003
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From: San Diego via Baton Rouge
charging problems diving me nuts!
i have a '77 f-100 and recently the battery wasn't charging. i thought it was the battery but it was checked and is fine. the next day i took the altenator off and had it bench tested (approximately 9 volts) so i replaced it and thought i solved the problem. by that night the battery's dead again. next i figure regulator so i change that and still won't charge.
i check my battery with volt meter and never get over 12 volts. today i exposed all wires from altenator and re-taped. of course that wasn't problem, but now is clean. i do light test on battery cable and post and show no short.
one more thing, i test resistence on f-terminal to ground and it flys to max (no resistence). i didnt test that when i first installed regulator and am wondering if i could have damaged that or altenator. sorry post is so long, i usually keep them short, but i wanted to include all info.
i have other info, but alerady too long
i check my battery with volt meter and never get over 12 volts. today i exposed all wires from altenator and re-taped. of course that wasn't problem, but now is clean. i do light test on battery cable and post and show no short.
one more thing, i test resistence on f-terminal to ground and it flys to max (no resistence). i didnt test that when i first installed regulator and am wondering if i could have damaged that or altenator. sorry post is so long, i usually keep them short, but i wanted to include all info.
i have other info, but alerady too long
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Junior User
Joined: Jun 2003
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From: San Diego via Baton Rouge
also, if it's some bad wires or ground or something like that. why was the whole system totally strong until i left my lights on all day at work and drained the battery ? thanks a ton.
Post Fiend
Joined: Apr 2002
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From: Central Kali
Measure the voltage at the fld (field) terminal of the alternator. If there is 0, the regulator or the wiring is bad. If you have around 11, the alternator is bad. The field terminal must have voltage for the alternator to start charging. 
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Junior User
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From: San Diego via Baton Rouge
thanks, i'm getting 0 at feild terminal so not altenator. also i checked for voltage coming out of regulator (orange feild wire), nothing. the regulators getting juice, so it would have to be bad regulator. it's new, but those things are kind of flukey. i guess i'll try to return.
before i take back though, i'd like to check resistence through regulator. but i don't know which terminals to check and what proper ohms should be, thanks.
before i take back though, i'd like to check resistence through regulator. but i don't know which terminals to check and what proper ohms should be, thanks.
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Junior User
Joined: Jun 2003
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From: San Diego via Baton Rouge
voltage regulator blues
i've been fighting a charging problem the last few days, and have narrowed it down to regulator/wiring. i'm getting juice to regulator (a terminal) but none out (f terminal). that would have to mean that regulators no good, right? it's new, but those things are flimsy, so i wouldn't be shocked if its no good.
before i take back though, i would like to check resistence through it, but i dont know which terminals to check between or proper ohmage. if someone knows where to find this info or can maybe offer some advice, i'd greatly appreciate. once again i want to thank creators of this site, i've used it several times and have no negative experiences.
before i take back though, i would like to check resistence through it, but i dont know which terminals to check between or proper ohmage. if someone knows where to find this info or can maybe offer some advice, i'd greatly appreciate. once again i want to thank creators of this site, i've used it several times and have no negative experiences.
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Junior User
Joined: Jun 2003
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From: San Diego via Baton Rouge
o.k., i just checked resistence between feild terminal and ground. that sucker shot to 0 (no resistence). obviously i have a shorted circuit. now i have no idea where to look, or if i can just cut out old feild wire to altenator and replace with new. any ideas appreciated.
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From: Virginia
I added your two post together to avoid confusion. I would test the field wiring with both ends disconnected(at the regulator and the alternator). This would make sure the wiring is good. I don't know what the resistance readings into the reg unit itself should be. If you want to test the alternator, take the field wire off and put 12 volts on the field terminal of the alternator for a few seconds. This will put the alt in full output. The voltage on the battery will swing way up, and the engine will probably slow a little bit.
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Post Fiend
Joined: Apr 2002
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From: Central Kali
If the field winding in the alternator is shorted to ground, it will blow the output transistor in the regulator. The field draws about 2 amps which would make it about 6 ohms.
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From: Virginia
If his field wiring in the alt is shorted to ground, and he does my test above, the situation could get a little exciting couldn't it?
I would expect a little spark, but if it acts like it's shorted, and the test field wire gets hot, then the field probably is shorted.
I would expect a little spark, but if it acts like it's shorted, and the test field wire gets hot, then the field probably is shorted.
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Junior User
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From: San Diego via Baton Rouge
thanks guys, i'm fixing to try a few things. i'm thinking that if i completely bypass the feild wire and the other wire that goes strait from altenator and regulator, that may fix me.
2 days troubleshooting, trial and erroring, and replacing every part remotely involved. why do i love it so much? haha
2 days troubleshooting, trial and erroring, and replacing every part remotely involved. why do i love it so much? haha
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Junior User
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From: San Diego via Baton Rouge
i thought i had something figured out, but now i'm disgusted. the wiring diagram i have in my haynes manuel is not what they did in my truck. the colors are same, but the diagram shows two wires going straight from alt. to reg. on my truck only the orange feild goes strait. the white/black runs up into cab. and the red/black runs strait to battery pos.
all the taping and stuff is factory. i'm sure its the same it just goes a different route.i'm tearing all tape and covers 'till i get to all the wires, test all links and fuses.
also that diagram was out of chilton manuel. i'll check haynes. i've found for some jobs the chilton is better, and some the haynes. oh well, i'll get it eventually. thanks
all the taping and stuff is factory. i'm sure its the same it just goes a different route.i'm tearing all tape and covers 'till i get to all the wires, test all links and fuses.
also that diagram was out of chilton manuel. i'll check haynes. i've found for some jobs the chilton is better, and some the haynes. oh well, i'll get it eventually. thanks
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