Very simple alternator question re: field terminals

patrick · Post by **patrick** » Sun May 11, 2008 2:06 am

Okay, so I bought a new engine harness (well, not recently; who puts their new parts on immediately?), and I can't remember if the wires that go to the two spade terminals on the alternator (one is labeled "GRD" and the other is labeled "FLD") can be reversed, or if the green and blue wires have to go to a specific terminal. For some reason, it's in the back of my mind that they can be reversed (inadvertently or otherwise), but it's been a while. The battery cable is obvious since it's big and circular and not a spade terminal.

Just so you know, I remembered that on the coil wire, brown is positive and black/yellow is negative. Do I get any credit? Haha...

Thanks for all input!

71440 gtx · Post by **71440 gtx** » Sun May 11, 2008 4:28 am

go here://www.mymopar.com/72to76_wiring.htm

73X · Post by **73X** » Sun May 11, 2008 4:33 am

Hook them up, if it charges, good. If not, swap them, your not going to hurt anything.

patrick · Post by **patrick** » Sun May 11, 2008 5:01 am

Interesting, in the wiring diagram at that site, both alternator terminals are labeled "F" (probably for "Field") and it doesn't specify a difference, so even though on mine one is labeled "GRD" and one is labeled "FLD" I'm just gonna presume it doesn't matter (bearing in mind we're not talking about the big ring-type battery terminal). Thanks guys! (But can't you walk into your garages/driveways and LOOK? LOL)

Smellslike1974 · Post by **Smellslike1974** » Sun May 11, 2008 11:27 am

Firefox doesnt know how to open your link....

landon1 · Post by **landon1** » Sun May 11, 2008 11:42 am

in my manual (not factory, mind you)....

it shows a dark green wire to voltage regulator that is dark green, coming from the spade closest to the engine. other spade is black and goes to fusible link, then to starter relay...maybe that helps - i believe i'm reading this right - been awhile - can't look at mine cuz it's been hacked on so much over the last 40 years

patrick · Post by **patrick** » Sun May 11, 2008 12:27 pm

landon1 wrote:in my manual (not factory, mind you)....

it shows a dark green wire to voltage regulator that is dark green, coming from the spade closest to the engine. other spade is black and goes to fusible link, then to starter relay...maybe that helps - i believe i'm reading this right - been awhile - can't look at mine cuz it's been hacked on so much over the last 40 years

40 years, huh? I smell a fish... You own a '68?

j/k, just yankin' your chain. Thanks for the help guys...

landon1 · Post by **landon1** » Sun May 11, 2008 5:33 pm

lol close enough to 40...bout twice as old as i am

72RoadRunnerGTX · Post by **72RoadRunnerGTX** » Mon May 12, 2008 12:17 am

The two field leads on an isolated field type alternator are interchangeable. Alternator will function correctly either way.

patrick · Post by **patrick** » Mon May 12, 2008 11:44 am

72RoadRunnerGTX wrote:The two field leads on an isolated field type alternator are interchangeable. Alternator will function correctly either way.

Now THAT's the answer I wanted!

Does this go for all Mopar-style "squareback" alternators? I have two spade-style terminal leads, but one is labeled GRD and the other is labeled FLD on the alternator. I presume this doesn't matter?

72RoadRunnerGTX · Post by **72RoadRunnerGTX** » Mon May 12, 2008 1:01 pm

Starting in 1970 Mopar went to an electronically regulated charging system. This change required both sides of the field circuit to be isolated from chassis ground, hence two field connectors rather than just one in the pre-70â€™ design. The 1972 diode pack redesign (commonly know as the â€œsquare-backâ€) continued on with the two isolated field connectors through the end of its production. I have seen the markings you have described; the regulator does control the negative side (green wire) of the field circuit as its function, while ignition voltage is applied to the other side of the field circuit (blue/white wire). Again, the alternator will operate regardless of the polarity of the field circuit. Later production alts. had both field terminals labeled â€œFLDâ€.