Replacement alternator wiring

[KTMonaco67]

Hi all,

I’m trying to replace the alternator in my 67’ Monaco but none of the replacements seem to match up exactly, wiring wise . The issue I’m running into is the existing alternator has a post with a nut on it near the engine mount . On the replacements , there is no post there. Is the post on the existing alternator a ground that someone added? Picture of the existing alternator and what a typical replacement looks like.

 

[Big_John]

That is an isolated field alternator with two field connections. Used from 1970 and up.

The 1969 and down alternator has one field connection with the other connection grounded internally.

To use the later alternator in an earlier car, one field connection needs to be grounded externally. So, that is a common "over the counter" replacement that has had one field connection grounded externally so it works on an earlier car.

 

[KTMonaco67]

That is an isolated field alternator with two field connections. Used from 1970 and up.

The 1969 and down alternator has one field connection with the other connection grounded internally.

To use the later alternator in an earlier car, one field connection needs to be grounded externally. So, that is a common "over the counter" replacement that has had one field connection grounded externally so it works on an earlier car.

Thank you very much for the info! So, if I’m understanding correctly I need to either find a way to externally ground the replacement or simply find a replacement that’s internally grounded?

 

[Big_John]

Thank you very much for the info! So, if I’m understanding correctly I need to either find a way to externally ground the replacement or simply find a replacement that’s internally grounded?

Basically, yes.

The earlier alternators are easily identified by a single field connection. The two alternators you show are also known as "square back" alternators and all the grounded field alternators are going to be "round back" style.

Both will work just fine, but the square back is a lot easier to replace the diodes.

 

[HWYCRZR]

It may already be grounded. Does the top terminal have a metal washer underneath the screw or a fiber/rubber washer underneath the screw? The right terminal by the BAT terminal should have a fiber or insulating washer where the top in your case should have a regular washer which will ground the terminal through the screw without the extra wire that you had above.

 

[72RoadRunnerGTX]

A ’69 and back alternator field terminal was not internally grounded, one brush was grounded through its mounting screw, and did not have a spade connection. The later dual isolated field alternators can be easily modified for an older application by removing the insulator under one of the brush mounting screws, substituting it for a conductive washer, again grounding the brush assembly via its mounting screw. Suggest too, clipping off the spade terminal on the grounded brush to avoid the ignition 1 field terminal wire from being accidently connected to the grounded brush.

 

[Big_John]

I need to either find a way to externally ground the replacement

Just so you understand, the wire in your top pic is the way the field is usually grounded.

 

[Big_John]

A ’69 and back alternator field terminal was not internally grounded

Very true, but I've found it's easier to say "internally grounded" rather than try to explain how one end of the field is grounded to the case.

It's been tough enough explaining that there isn't two fields because of the two field connections, so that slightly incorrect description that a lot of others use just makes it understandable.

 

[HWYCRZR]

@Big_John is there any real advantage to grounding with an additional wire to the case vs directly grounding it with a metal washer and the screw? Mine has been grounded with a washer since at least the mid ‘80’s. And the terminal was clipped.

 

[Big_John]

@Big_John is there any real advantage to grounding with an additional wire to the case vs directly grounding it with a metal washer and the screw? Mine has been grounded with a washer since at least the mid ‘80’s. And the terminal was clipped.

None. It's just a little easier to explain and for some to do.