Alternator Questions

[Bowtie T]

Just got my T on the road. I've been driving it a little and I don't think my alternator is charging the battery. I probably don't have it hooked up right. Looking at the back of the alternator, there is the battery lug on the left, ground on the right, in the middle are 2 prongs marked R & F. What are these for? Do they need to be hooked up? I had the alternator checked and they said it was good? Any help appreciated. I will try to post a picture if need be.

 

[ellis8500]

You will have to tell us what alternator you have. GM? Ford?

 

[choppedtop]

You probably need a switched wire to excite the alternator. And you may need a diode in the same wire to prevent feed back if your not running a idiot light. Not sure which prong to use without looking at mine. Guessing of course that it is a internal regulated alt. My thought is the field has to be excited, so that would be the F lug. I would take it to you local parts store, and they can tell you for sure, when they test it. Before I put in a diode, on one car, the electric fan would feed back and not let the car shut down.

 

[Intrepid]

I am use the GM ones that have B F S ,, B = Bat Charge circuit, this should be the big wire going back to your fuse panel, some guys run this right back to the battery but not recommended. F= Field ..If I remember correctly, this can be jumped over to the bat wire but normally comes from the fuse panel to an indicator light, then to the F pin, (so if the light is on you have an issue). S= Sense .. If I remember correctly this can be left off when trying to just run a one wire circuit, but should come from the fuse panel, this lets the alternator adjust the voltage output according to the voltage drop if say you turn the headlights on, or plug in a lighter.
Allot of hot rod guys use the 3 wire alternator and just rig it as a single wire, but it makes no sense to me, if you have the options there to allow things to run better why wouldn't you use it.

 

[Intrepid]

It just occurred to me that I should have posted my drawings somewhere easy to find, to I will post them in the Tech Section in Electrical.

 

[Bowtie T]

You will have to tell us what alternator you have. GM? Ford?

Sorry Bill, It is GM. Looking at the diagram in the "How to wire your hotrod book", it looks just like the "Pre-'69" alt. The engine is a '80-'85 350

 

[Bowtie T]

You probably need a switched wire to excite the alternator. And you may need a diode in the same wire to prevent feed back if your not running a idiot light. Not sure which prong to use without looking at mine. Guessing of course that it is a internal regulated alt. My thought is the field has to be excited, so that would be the F lug. I would take it to you local parts store, and they can tell you for sure, when they test it. Before I put in a diode, on one car, the electric fan would feed back and not let the car shut down.

Thanks choppedtop. I don't know about taking it back to the auto parts store, I had to go to 3 places before I could get one to check it, Then it took 3 people & about 20 minutes!

 

[choppedtop]

Oh my. sounds like they have "new generation" parts people. Going to go look at my setups, now to see if they have R and F or 1 and 2 markings. Did you ever determine what make alt your have?

 

[choppedtop]

Darn,,,edit time got me. 2 of my alts are wired as follows. 10ga wire from alt to battery. This also has a jumper from big post on alt to 2/F Switched 12 volts 16ga wire to #1/R with diode.
Here is a picture I snagged from another site. The 10ga wire shown can be run straight to starter hot post instead of terminal block.
Technical - Alternator question

 

[RPM]

You don't need a diode if you will run that wire to the Acc side of the ignition switch.

 

[choppedtop]

Ron, are you saying the acc side is hot when switch is in the on position? I guess that I have never checked it for that. Good to have all this knowledge available.
Lee

 

[RPM]

Yes it is hot when the ignition is on. That separates the alternator from the ignition.

 

[Bowtie T]

I tried wiring it like ya'll suggested and it blew the fuse to my ignition. After a little more research, it is a pre 69' without a voltage regulator. No telling how many amps it was charging when I started it up.
Went to the parts store and bought a single wire unit. $45 and problem solved. Also only one wire to run instead of 3.
Thanks for you help guys. BTW, anyone need a pre 69' alt. that uses external reg? JK