Alternator Help for 1969 RR

[superbird77]

Help! I am by no means an electrical guru so bear with me. I have a 1969 Roadrunner, i put a new electronic ignition wiring harness on it FYI. I also used a new pre 1970 stock looking black box regulator with solid state internals. My question is regarding the proper alternator or possibly an upgraded amperage version to maybe avoid my lights dimming at idle. I am confused on single field versus dual field and if i can upgrade to a higher amp alternator. Where does the second wire come from if i use a dual field version? I'll admit i know next to nothing about charging systems. What do you guys recommend for something like this? What would be my best setup?

 

[hashmaker]

I had the same problem 2 years ago. I bought a new alt. for NAPA which turned out to be a two field alt. In the course of hooking it up I learned that the 70 and newer used the 2 field wire and 69 on back used one. But the 70 put out more power. If I remember (it sounds crazy) we grounded the other field wire and the alt. started putting out and has been working fine ever since.

 

[440+6]

Yes you just ground the second feild to the alt case.
What fixed my lights is putting a smaller pulley on the alternator, I went from 3.5 to 3.25 inch

 

[Ranger16]

I no longer have the dimming headlamp problem after replacing my alternator, but I think the biggest help was cleaning all the electrical contacts on the alt, bulkhead connectors and starter solenoid. I upped the alternator from the factory 38 amp to a 55 amp, but not sure if that played into the improvement very much.

 

[oldbee]

What everyone else has said; with no 'super' add-on loads you'll be fine. Just ground the 2nd field term.

 

[RJRENTON]

The 2 field connection alternator operation is very similar to the single field connection unit.
In the 2 field connection alternator, the 12 volt rotor supply current goes through the rotating field connections (brushes) back to the voltage regulator. Inside the voltage regulator, the main component is a switching transistor, which when it turns on, grounds the alternator field causing the alternator to charge. There is a voltage divider network which monitors system voltage and turns on and off the switching transistor, which in turn, turns on and off the alternator's field current to maintain system voltage.
The old system, varied the field current by physically turning on and off to an average voltage determined by the internal tension of the spring. The opening closing operation of the points caused them to pit and ultimately fail. The new system does the same except with no moving parts and more accurately.
Some aftermarket suppliers sell a transistorized unit to look like the original Mopar regulator for use with single wire systems.
Bob Renton

 

[Nacho-RT74]

the difference between "single field" and "dual field" alts is just the pole is being driven my the regulator.

"single fields" ( tipically roundbacks ) are regulated by the positive pole being feeded from the regulator, as mentioned switching on-off this field to get the regulated source. Negative is constant being the brush attached directly to the chassis without a prong to be wired

"dual fields"(tipically squarebacks ) are regulated the same BUT negative is the source being sourced by the regulator, not anymore positive. So this is the reason why these alts gets TWO PRONGS to feed BOTH ISOLATED brushes. This time the constant source is sourced via the RUN circuit ( blue wire ) from ign switch

on both systems the regulated source is the green wire, but as mentioned, positive on single fields and negative on dual fields

actually the therm single and dual "fields" is inaccurated, since all alternators get dual fields ( if not wasn't imposible to make them work ). The more accurate therm could be single or dual prongs, or field WIRES.

You can become a dual field into a single easilly. Just need to ground one of the brushes. You can use a jumper wire to chassis or replace the isolation washer to the brush for a metallic one. You can also bend the prong and fold it down the isolation brush housing somehow, making contact with alt case

You can also become a single field alt into a dual one, although a bit more job involved... dril couple of holes on rear case and get the isolated brush set to install it and remove the grounded brush.

althought roundbacks are tipically single field, since the squarebacks ( all are dual ) began in 72 and electronic reg system with dual wired fields began on 70, then you'll find 70/71 alts which being round backs are dual field OR even able to get both setups ( rear case already casted to accept dual or single setups )

as mentioned a more powerfull alt allong with smaller pulley on it and a GOOD INTENSE mantenience on all the electrical system FROM END TO END, including the ammeter gauge outside and inside, will help on get a nice feeding/charging capacity. Bigger upgrades are able to do it with thicker wire paths, bypassing bulkhead conectors on charging wires are really helpfull to, but also will depend if you really need it because is a heavy equipped car or a driver.

 

[superbird77]

Thank you very much guys, I now understand the difference and will be purchasing the proper alternator asap.

 

[Nacho-RT74]

and, about the more output from later squarebacks, that could be a debate... there are 50 amps or so roundbacks ( specially those 70/71 mentioned ) alts too like some squarebacks. The design or setup makes no diff really, like just the demand on later cars for a more powerfull systems what arrived together with the design and system change of the alts. Then entering on 80s, squarebacks began to reach 78 amps output, although these got also some changes with wider stators and some housing size changes. But still some of these were 55-60 amps

50-55 amps alts are still not enough really. Thats the max output ( over 1800-2000 engine RPMs ) they reach, and tipically a fairlly stock car with AC will demand just that IDDLING when you turn on the AC ( not necesarilly at max speed ), at night stopped at traffic light, geared and brakes pressed. Not to mention if raining and wipers on.

 

[RM23M9A]

So with Electronic Ignition Year One send out a 2 wire (Blue & Green Field wire) harness.. My alt which is new/ Rebuilt, does not charge. So got out the voltmeter. Did a couple of tests. In the past, the green wire was always attatched to the tap nearest the TOP of Alt. Furthest away from BATT termninal. Reading 00.1/00.0 Ohms,

the 2nd tab obviously has 16 Ohms!

When hooked up, blue wire began to overheat. This blue wire runs thru Ballast toward bulkhead with no apparent place to pigtail it into! However, it's HOT. So? Green wire to 0.0 Ohm tab or 16 Ohm tab. Being HOT, seems confusing! This wire's supposed to run to Ign lead on Ign switch as well? Sounds as of ONE must not be used?
Then theres this YELLOW wire runs off of the "I" tab of starter relay.. No clue there. Im about to go back to points. Year one Needs a damn schematic! Or this that alternator diagram with HU199BM Harness sold.

Thanks a BUNCH!!!

 

[Nacho-RT74]

brush grounded to work like a single field alt or it is somehow shorted... If you test both prongs will get same 16 ohms measure... or close. Both prongs must be completelly isolated from chassis and no measure againts it. Just get the rotor impedance between both prongs.

I think 16 ohms is way too much though. It should be more like 5-8 ohms as far I recall ? can't remember

what regulator are you using ? electronic stock one ?

blue wire is Ign1 circuit ( positive )

Green wire is the circuit closing with VR ground and is the regulated side

yellow wire is Crank signal to starter relay and is an independient one from the rest

Ignition and charging circuit are linked by the blue wire signal but they work separatelly one from the other. So getting back to points will make nothing to the charging circuit

 

[dadsbee]

What I told him yesterday Nacho... where he is hooking up the Blue + wire is grounded to the case and why he's frying his blue wire as it's a dead short. He needs to get that spade connection isolated from the case, but of course it shouldn't have been grounded out in the first place if he wants to stick with the two field system and the electronic regulator. It would work just fine on a single green wire system...

 

[Nacho-RT74]

Yeap. But a dead short should already melt down the wire somewhere up to get smoke! Or blow the fuse link. I have been there. My car didn't have fuse link but a regular wire when I got it, the brush got accidentally grounded and melted the blue wire cover up to the cluster! ( standard cluster gets the blue source to the PCB ). Had to replace all the wire and some others around it.

 

[dadsbee]

Oh his wires have melted...