I just installed a set of under drive pulleys on my truck and i cant get the alt to charge until i hit about 3000 rpm. I can ground the field terminal instantanely and it will start charging right away really dont want to put a push button swith to ground the wire any other ideas out there. thanks in advance for your help.

 

Knowing the Make, Model, year and if possible the style of alternator that is on your vehicle is needed to properly lead you into the correct area of the problem, but all underdrive pulleys cause the alternator to turn slower which in effect does not produce the correct amount of AC voltage out of the stator tap terminal to the regulator to turn the regulator on, so what is mostly needed here is to get the RPM's back up on the alternator where they were before you installed the underdrive pulley setup, but if I knew the Make, model and Year and if possible the style of alternator, I might be able to lead you down another path to make it function without changing the underdrive pulley back or looking for a smaller alternator pulley to make it turn faster. Electric1

 

Thanks for responding Electric 1 the vehicle is a 1973 ford f-100 with a ford alt 63 amp single wire thanks for your help chuck

 

I need to know one more thing, sorry it is taking me way to long to respond to you, there is two wiring diagrams for Ford External Regulator, one with the Voltmeter and one with the idiot light,
The Alternator with the Voltmeter in the dash uses the ignition power to turn the regulator on. The power to turn this circuit on is the green with red stipe (s) terminal at the regulator, also the (I) terminal at the regulator is not used, so heres the story.

(F) terminal at the regulator goes to Field at Alternator center reart terminal, ( white wire)

(S) terminal at the regulator goes to ignition swith, powered by 12 volts to turn the regulator on with the ignition key. (green/red str)

(A+) terminal at the regulator (yellow wire) from battery positive.

(I) terminal not used at the regulator.

(CASE) ground

Second wiring diagram with idiot light. Uses all four wires at the regulator.

(F) terminal at the regulator goes to the alternator (white wire)

(S) terminal at the regulator goes to the alternator (white/ blk str)
this wire turns the regulator on at a high rpm when the low rpm portion is not functioning.

(A+) terminal at the regulator goes to Battery positive, (yellow)

(I) terminal goes to charge indicator light to the ignition switch. There is also a 15 ohm resisitor bypassing the indicator light just incase the light blows out to let the power still go through to the (I) terminal at the regulator. (green/red stripe)this wire turns the alternator on at a low rpm.

With this wiring diagram, key on engine off, power to be at (I and
A+) terminal with regulator unplugged,

with vehicle running, AC voltage to be approx. 7 volts at (S) terminal with regulator plugged into harness,

If you have all of this, unplug regulator with vehicle running and jumper (F) terminal to (A+) terminal voltage at battery should go above 14 volts DC, if so replace regulator, I have a hunch that the (I) terminal section of the regulator inside is not functioning,
I hope this helps you blueprint your Alternator circuit, Electric1

 

hey electric 1 my alt is single wire it has a 12 volt feed from battery has a built in aftermarket voltage regulator I can ground the field wire instantly and it will start charging its either that or rev it up to 3000rpm to kick it in really like the pulley set up hate to change it.
thanks for your help!!! chuck

 

Chuck, now you said you had a 63 amp Ford, now if I am right here, Ford does not manufacture a 63 amp Ford unit, Delco Remy did but not Ford, You also mentioned this time you had a one wire alternator, why did you not state this before, One wire alternators use the Stator power through the windings feeding out the (s) terminal to the regulator to turn the alternator on. Ford also did not manufacture an internal regulated unit until the mid 1980's, now which is it? If you have a Delco Remy, (which from what you say this time you do)???? the regulator has to be changed to a different type, take it to an Electric Rebuilder and get them to install a Transpo D10AC regulator inside the alternator, it turns on at a much lower RPM than the original Transpo D10SE regulator, this regulator turns on the Delco Remy alternator on in a John Deere A, which by the way turns very slow. Hope this help more, Electric1

 

Hey electric 1 If you read my 2nd responce to you I stated that it had a single wire it is a ford alt i was told it was a 63 amp maybe the 65 year old alt rebuilder doesnt know what he,s talking about??? the alt has a transpo f707b regulator it is not a delco remy. Thats all the info i have thanks for any help!

 

Shortbed, your right, I can't read but I am not alone, the number of the Transpo Regulator is not an F707B but an F7078, and it is not a built in but a bolt on. I will find you the answer to your question on Monday. You have, I believe three choices to go from here, I think your best choice might be to go back to the external fender mounted regulator, because it is an ignition key turn on, but I will check for you. As far as the 65 year old rebuilder, I am not going to get into a pissing match here, but Ford as I now has never posted a small frame Ford alternator as a 63 amp unit,.... ever, 40 and 60 amp only. Ford also does not and has never made a built in regulator (inside) the alternator,....ever. I was trying to read what you wrote and it was unclear as to what you had that I could not see. One wire 63 amp built in regulator is not a Ford alternator over the Phone or E-mail, regardless of age. Electric1 I'll be back

 

Shortbed here you go, your going to have to remove the F7078 regulator and go back to the fender mounted regulator wired in the fashion stated above. The underdrive pulley is what is the problem, but to keep the underdrive you are going to have to change the regulator and add wiring. Soory it took so long. Electric1