Alternator overcharging

[SteveJ]

5 hours ago, chaseincats said:

No but the problem is always fixed after the swap which is why I think it’s always the alternator

But have you checked battery sense voltage at the alternator?

[chaseincats]

2 minutes ago, SteveJ said:

But have you checked battery sense voltage at the alternator?

I haven’t, how would I do that?

[SteveJ]

Measure voltage to ground on the backside of the connector. One pin should have voltage with the engine off. That is the battery sense. Also, look to see if the connector is corroded.

[Captain Obvious]

10 hours ago, chaseincats said:

No but the problem is always fixed after the swap which is why I think it’s always the alternator

I'm thinking there's a possibility you have an intermittent connection and when you move the wiring harness around to change the alternator, maybe you're temporarily bettering the connection.

For the 78-83 alternator system, there should be two W/R wires going to the back of the alternator that are always hot. One big, and one small. The big W/R is power output from the alternator and the small W/R is the sense line. Those two W/R wires are connected together inside the wiring harness. I've heard of other owners finding that the connection between the two (buried in the harness) corrodes over time and becomes intermittent.

That, or as SteveJ suggested above, maybe the contact(s) inside the two position connector on the back of the alternator is flaky dirty intermittent.

[Captain Obvious]

Couple more thoughts on your alternator thing...

First, if you find the overcharging issue happening again, you can take voltage measurements from both of those W/R wires on the back of the alternator. They should be identical (because they are supposed to be hard connected together inside the harness). If you find 15.5 on the large W/R and 12.5 on the small, then you've got a problem with that connection.

Second, it IS of course possible that you've had multiple voltage regulator failures on multiple alternators. However, as the number of them goes up, the likelihood that you're got something else going on goes up as well.

[Zed Head]

On 6/20/2023 at 8:08 AM, chaseincats said:

No but the problem is always fixed after the swap which is why I think it’s always the alternator

Did O'Reilly's test the alternators before replacing, or did they just swap them without testing?

Adding on to CO's point - maybe you have an intermittent connection that is actually damaging the alternators.  The alternators really are bad but it's your car that broke them.  They're already weak because the reman shops keep the old parts that still function.

I think that the S wire might be connected to the WR fusible link wire by one of those metal butt connector splices buried in the harness.  The ones that look like a PO's hack job.  Might be worthwhile to peel the harness open and check it out.  My 76 harness had a bunch of melty fused wires buried in it from some previous catastrophe.

[Zed Head]

Also, never really noticed it before, but Nissan put a nice description of the regulator in the FSM.  They even supplied a circuit schematic.  It's not my field but still pretty cool to ponder.

 

[Zed Head]

Here's a clue about the quality of the typical reman alternator.  Some of the repair parts cost more than a whole reman.

https://www.rockauto.com/en/moreinfo.php?pk=45765&cc=1209260&pt=4884&jsn=394

[chaseincats]

Sorry for the lack of response, all - I've been out of town and just got back.

When measuring the sense line to ground (I'll use the negative battery terminal), does the car have to be off, in accessory mode, or running?

 

@Zed Head I don't believe O'Reilly's tests the alternators they get from their reman folks but I could be wrong.

Edited July 3, 2023 by chaseincats

[Captain Obvious]

I would think the highest amount of info would come from two readings... 1) With the engine off, and 2) While the problem is occurring and the engine is running. 

And just to be able to keep the analysis simple... I'd measure it to the alternator body (ground on the body itself).

[chaseincats]

39 minutes ago, Captain Obvious said:

I would think the highest amount of info would come from two readings... 1) With the engine off, and 2) While the problem is occurring and the engine is running. 

And just to be able to keep the analysis simple... I'd measure it to the alternator body (ground on the body itself).

Gotcha, so I just took a reading from the alternator body to the small r/w wire which is a bullet connector that isn't connected.  I never connected this and just assumed it was a remnant of the 77 and back cars that were externally regulated.

Anyway, the voltage from that wire to the alternator body is identical to the battery 12.25v

The other w/r wire looks to be a ring terminal and is also sitting at 12.25v

Edited July 3, 2023 by chaseincats

[SteveJ]

What white/red isn't connected? A photo or two would help. If your alternator isn't getting the sense voltage it would overcharge, just as @Captain Obvious said.