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Alternator question

69'Net

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Probably been asked alot but i couldnt find my answer. Im currently changing a 69 plymouth to the newer style system with the orange box and regulator. I have a brand new square back alternator that came with a different car that I was going to use on it. It has two "field" tabs on the back, but one tab has a ridge on it so you can't put a connector on it. Is this actually a single field that's been rebuilt? Is there a way to check?
 
The second tab with the ridges could be internally grounded. But, to be sure, you could solder a wire to it and ground it. It won't hurt anything.
 
Well if I'm understanding this correctly, that would make it a single field right? I need a dual field
 
Probably been asked alot but i couldnt find my answer. Im currently changing a 69 plymouth to the newer style system with the orange box and regulator. I have a brand new square back alternator that came with a different car that I was going to use on it. It has two "field" tabs on the back, but one tab has a ridge on it so you can't put a connector on it. Is this actually a single field that's been rebuilt? Is there a way to check?
Pix please......all alternators have two brushes.....origional round back units only have and use one connection. 1970-72 round back units use both ungrounded brushes and an electronic voltage regulator. Later square back alternators use both ungrounded brushes and an electronic voltage regulator. Most "rebuilt-replacement" units are of the square back design and with a minor modification to one of the brush holders, can be adapted to use on either old style mechanical voltage regulator system (one brush connection) or electronic voltage regulator system (both brush connections). Pictures of your installation would be helpful in offering guidance........just my opinion of course...
BOB RENTON
 
Here's a photo

20230513_203730.jpg
 
It appears that the silver colored brush is grounded thru its mounting screw. Were there any instructions for wiring connections to use with a two wire field and electronic voltage regulator system?? Usually there Is an insulating bushing and screw retainer to UNGROUND the brush holder/connection and to isolate that brush from ground....to make it an isolated field unit. Do you have a factory service manual with the details shown....
BOB RENTON
 
No instructions. I do have a service manual, but its for 1969
 
Two prong roundbacks are 70/71… 72s were already squarebacks.


——————-

about I can see on pic is a squareback already modified to work as a “single field” for pre 70 models on stock form. I can see the brush silver prong already cut to save from connect any wire there if its already grounded. If you look closely to the assembly, the retaining screw for that field prong must get a metalic washer underneath to ground the brush, while the gold prong must get an isolation washer (I can see the brownish washer there) between screw and prong keeping the brush isolated. That’s the prong the wire coming from regulator (green in this case ) will be connected.

interesting deal here, two diff colors on prongs. I can’t recall gold terminals for them.

I can see also the alternator is the “revised” version of the squarebacks used from late 70’s and 80’s with stator being hidded down the case, which is a bit wider than the earlier alts. This guarantees is AT LEAST a 60 amps unit. Which is good against all roundbacks and most earlier squarebacks.


NOW, if you want to “reconvert” this unit to a “dual field” just need to replace the brush since the prong was cut and install the isolation washer for it… and done.

they are easy to find
 
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Tipically found in pair… this on a quick search

Advance Auto Parts - Down for Maintenance

i bet searching around can be found even cheaper.

take care of the isolation holder, if still gets the shoulder working as bushing for the prong. Sometimes can be also broken when grounding the brush. If so, the holder would need to be replaced too…

this would be the correct set for that alt
Brush Set Alternator 78-83, 23,46 €

not this one, which even brushes and the ”affected” holder are the same, the other holder is not, so getting the right one you still get a spare holder for your new alt
Brush Set Alternator 70-78, 13,54 €

I’m searching from Spain, so most of my searchs (being quick) floats on Europe shops… I’m just copying and pasting these links as a reference, but they can be found the same on local shops.

I bet the single brush, isolation washer and (if need it) isolation holder can be found as a unit and not the full kit, but I’m just providing the full info
 
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You guys are awesome thank you!
 
It seems it already has the brushes and isolators in it?

20230514_092222.jpg
 
No instructions. I do have a service manual, but its for 1969
Suggest to obtain a copy (available on line at no cost) of a 1972 or later factory service manual (FSM) that shows an exploded view of the alternator's brushes and the pieces used to isolate the brush holders from the case (ground).....OR.... take your alternator to your favorite auto parts store and ask them to show you how to UNGROUND the brush holder.....which may require to BUY a replacement brush & brush holder assembly.....inexpensive....less than $20. Standard Motor Products, or equal, makes the parts you need.
BOB RENTON
 
It seems it already has the brushes and isolators in it?

View attachment 1464863
The BLACK colored washer, shown in the lower pix, needs to be installed UNDER the the head of the the screw of the GOLD colored wire connector of the upper brush holder shown in the upper pix. The washer isolates the connection from the case (ground) making what you have an isolated field alternator.......do not over tighten the mounting screws as the materials are somewhat fragile. One at a time, Check continuity from the wire connector to the alternator case.....there should be NO CONTINUITY.....
BOB RENTON
 
Yes, definitelly is weird both screws got the isolation washer. However since the brush holder is broken and the prong was cut, it’s time for the kit. The autozone link I posted with the kit will be pretty much enough since it got everything.

once everything is installed back, as mentioned, both brushes must be isolated from ground. Making a continuity test is easy. You should be able to get reading between brushes ( when I have made that test, I have got around 4.5-5.5 ohms as far I recall ) and no measure between any of the brush prongs and chassis.

then when alt is back to the engine, either wires ( blue and green ) to the alt fields on engine harness can be connected to any of the brushes.
 
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