Hot alternator wire

[MAXSDAD]

Did some searching, but couldn't find anything specific to my issue.
Background - FJ40 with 350. Voltage at battery with engine running was around 12.25 - suspected the alternator, so got replacement
Alternator does not have internal regulator.
After the alternator swap there was no difference in voltage.
Also after the swap, I noticed that the white/black wire on the alternator plug (comes from VR) gets very hot - hot enough to melt the plug.
Any ideas why?
Thanks in advance.

 

[cardinal fang]

Go here and see if that helps.

 

[74fj40]

Thanks, but don't think it's the same - my alternator plug has 2 wires - R and F, plus there's a Batt and Grd terminals on the alternator itself.
The current wiring has the large white/blue wire from the ammeter hooked to the Batt terminal, nothing hooked up to the Grd terminal, the white/black wire in the plug to R and the white/green wire at the plug to F.

Go here and see if that helps.

 

[Poser]

GM or Toyota alt?


Post up a pic of the alt....

 

[Pin_Head]

Not sure what type of alternator you have there, but if the white/black stripe wire is original Toyota, it is a ground wire and I don't think that this should be connected to the R terminal. I'm not sure what the R terminal is, but I'm guessing that it is the common connection of the wye wound stator that is often used to run the idiot light. Grounding this would inactivate the alternator and cause the wire to burn as you describe.

 

[MAXSDAD]

It's a GM alternator with original Toyota VR and wiring.

 

[honk]

You don't want that batt to ammeter connection - I'm surprised you haven't smoked it already. The battery connection should be wired to the battery positive terminal. The green field (F) comes from the voltage regulator - usually also a green wire with an 'F' terminal marking. The 'R' terminal is as above in an external regulator system.
T

 

[Poser]

Alternator does not have internal regulator.

You know this to be fact?





I have seen that style with an internal regulator...and would far prefer that over the Toyota unit.....but that is just me.


This new alt came with a 'pigtail' that you were supposed to connect to the existing wiring, or are you using existing plug/wiring?

Are you positive that the alt you removed was not internally regulated?

 

[74fj40]

No, not positive that it isn't internally regulated - got the replacement at NAPA - the salesman told us it was externally regulated. Is there a reasonably easy way to tell?
We used the existing wiring (doesn't mean it was correct - there was a PO involved!!)

You know this to be fact?





I have seen that style with an internal regulator...and would far prefer that over the Toyota unit.....but that is just me.


This new alt came with a 'pigtail' that you were supposed to connect to the existing wiring, or are you using existing plug/wiring?

Are you positive that the alt you removed was not internally regulated?

 

[Pin_Head]

I'm not sure what type of alternator that is, but it seems to predate the 10Si, which was the first GM internally regulated alternator.

If the wiring is stock, for sure the white wire with black stripe is a ground wire and it does not connect to the alternator plug, only to the ground lug. Disconnect it and see if the problem goes away.

The only wires you need to run it are the B+ wire to the batt terminal and the white/green field wire that goes tothe F terminal.

In view of its age it is unlikely to put out more power than the stock amp meter can handle, so I wouldn't worry about rewiring the output if you haven't burned out the amp meter yet.

Edit: Yes, it is an early externally regulated type:

http://www.rowand.net/Shop/Tech/GmAlternatorIdentification.htm

 

[theo]

The only wires you need to run it are the B+ wire to the batt terminal and the white/green field wire that goes tothe F terminal.

Edit: Yes, it is an early externally regulated type:

http://www.rowand.net/Shop/Tech/GmAlternatorIdentification.htm

Thanks, Pin. Well done. I have a question though. Don't the vibrating point style regulators do their work by controlling the degree to which the field windings are grounded? And if so, doesn't he need the ground connection between the alternator and regulator? Seems like without it the alternator output will be zero.

 

[Pin_Head]

No, the wire is redundant because the alternator case is grounded.

Toyota provided a ground wire on some years as insurance that the voltage regulator and alternator would share the same ground even if the chassis ground became corroded or had a bad connection. .

 

[74fj40]

Thanks - made some progress.
Hooked the B+ directly to the battery, the white/black wire directly to the ground and the white/green to field.
Don't know what to do with the white/blue wire from the ammeter.
13.5 at the battery - some of the time - the rest of the time, it's about 12.8 - had the alternator tested - it's ok. Th alternator makes a sort of whining noise when reading 13.5 and doesn't make the noise when it reads 12.8.
Could my VR be bad, or might there be something else I've overlooked?
Thanks.

I'm not sure what type of alternator that is, but it seems to predate the 10Si, which was the first GM internally regulated alternator.

If the wiring is stock, for sure the white wire with black stripe is a ground wire and it does not connect to the alternator plug, only to the ground lug. Disconnect it and see if the problem goes away.

The only wires you need to run it are the B+ wire to the batt terminal and the white/green field wire that goes tothe F terminal.

In view of its age it is unlikely to put out more power than the stock amp meter can handle, so I wouldn't worry about rewiring the output if you haven't burned out the amp meter yet.

Edit: Yes, it is an early externally regulated type:

http://www.rowand.net/Shop/Tech/GmAlternatorIdentification.htm

 

[Pin_Head]

Sounds like it is working.

I would remove the direct connect to the battery and reinstall the large white/blue stripe wire at the Bat lug because:

1. It will protect your alternator and battery from potential catastrophic failure if it shorts out because the stock wire has a fusible link.

2. The old GM alternator does not put out more power than the Toy alternator, so you are not risking frying your amp meter.

3. The amp meter will work properly.