Dual Field Alternator To Single Field..Help...

My Goddaughter's in Tucson with her '70 Duster 318; I'm in San Diego.

She called today saying her battery isn't charging. Her aftermarket in-dash volt meter reads 11 volts with the motor running.

Long story short, she found the battery stud on the back of the dual field alternator has somehow snapped off and the wire was just hanging loose.

Ok, so her local Autozone has a single field alt in stock. She gets it swapped out and doesn't know which field wire to hook up, so I told her she can use either one.

Now at idle she's charging fine, but at cruising speed and up the gauge is almost pegged at over 16+ volts, and she's getting some occasional smoke in the car.

I'm guessing my "either one" advice was wrong? Does it matter? What to do with the unused wire? She's at soccer practice now and she's worried about driving home at night..

Get that alternator off there now and get the correct one. Don't drive it unless the wires are unhooked. Its not charging right.My bets there is more damage done.

In general, dual field alternator in a single field application with single field VR is easy... just ground one field terminal.

The other way, single field alternator in dual field application, not so much.

Easiest to stop at another AP store... they should have some flavor of dual field in stock. Anything from a '70 roundback dual field rated 50 amps up to a late square back rated 78 amps should get her home. Also a good idea to pick up a regulator in case the current one is fried.

They only list the single field alternator for the older cars. I ended up buying one for a 86 diplomat.. Works well. Kevin

#1 do not even start the car with it full fielding like that, dont even consider it. call whomever is helping her & ask them to swap the same "location" brush from the dual field terminal later OE alt that has the broke "batt" stud over to the single field terminal early alt they mistakenly sold her, to convert the single field terminal alt to a dual field terminal alt. both alts have 2 "ends" on the single field circuit but the early one, the terminal has no male lug for the blue wire plus it is grounded to the case. you are subbing in an ungrounded (insulated) brush/brush holder from the later alt to the early alt so you can plug in both blue/green field terminal wires. No comment if the hard components are still functioning but your odds are good. (DONT start eng). use the fiber washers etc from the old one so the added brush/brush holder ain't grounded to the case square metal nub that it bolts to. duplicate the no continuity to ground condition of the orig one

You cant do that with all alternators. They should return the wrong and get the right one. They sold her a 69 or older.

And if there was smoke in the car the dash harness has burned along the power wire path. Hahe the engine harness pulled from the bulkhead connection and check the black 12 gauge wire connection it may have melted. Inner dash harness should be checked also.

I agree they should have sold her the correct one & I can see how a non Mopar dwebe counter parts house newbie coulda got it wrong with 69/70 being the cutoff/switch year. gonna be interesting how it transpires with the general across the board parts house policy of no return on electrical parts. on swapping holders take the one off on both of em & visual of the case nub/brass contact ring below will tell you in seconds if you can change em out. Do ya feel lucky? well do ya. Holler how it turns out

Pretty sure you can upgrade most any single field to a dual field. You just need to change the grounded terminal brush to an isolated type. New brushes cost about 6 bucks.

Good info here

Using the green wire would result in no charge but using the blue wire amounts to a near dead short to ground....thus the smoke.

Once again you cant do that with all alternators. Most all pre 70 cases wont accept an isolated brush holder.

You can if you modify the case slightly.

UPDATE : She made it home last night trying to keep the rpm low so as not to peg the gauge.

This morning I called her Autozone and verified that they had a dual field square back alternator in stock (had to explain in simplest terms to the dude what to look for) and a new regulator. Yep, they have them both.

She just went over and swapped 'em both at the same time in their parking lot (with lots of "Hey, you need any help?")...

Anyway, she hooked the battery back up, lit it off, and now has a steady +14v on the meter regardless of RPM and no smoke/burning smell.

Almost forgot - have to give Autozone some props; they took back and credited her for the incorrect one they gave her, no problem.

Many thanks to everybody that chimed in.

Right. My point was that most all pre 70 cases wont accept a insulated brush holder as a simple bolt on. But the MAIN point is the young girl paid for an item she should not need to modify to make it work. They sold her the wrong one and she is lucky that there was not damage done by running it. Looks like the problem is fixed.