Melted wire coming off alternator

[882993md]

Hi everyone, I discovered this wire had melted. As you can see from the attached pictures it leads to the T shaped plug that goes into the alternator. I can splice in a new wire but I'm clueless why this happened. I also found this blown 10 amp fuse in the fuse block. (Ignore the tissue paper I was just using it as background for photo clarity). Howard 1974 260z

[gogriz91]

I wonder if your voltage regulator is bad?

[882993md]

Thanks gogriz. Im reviewing testing the voltage regulator in the service manual.

Edited October 1, 2016 by 882993md

[beermanpete]

Does your car have an alternator upgrade installed? The wiring does not look like it matches the 260Z schematic.

[882993md]

On 10/1/2016 at 11:34 PM, beermanpete said:

Does your car have an alternator upgrade installed? The wiring does not look like it matches the 260Z schematic.

Beermanpete,

I have the Hitachi alternator which I believe is stock. The po did upgrade the wiring with relays. 

[Zed Head]

I don't know the details but I think that SteveJ probably does, about how the fuel pump relay is powered from the voltage regulator.  I think the the N pin on the back of the alternator powers the relay so that the pump only runs when the engine is running.  And that small fuse block you show might be the fuel pump fuse, or it might be the one that blew (can't tell which is which is your pictures).  In short, you might have a shorted fuel pump wire or fuel pump relay wire.  Just a guess.  I looked through the FSM and found some things that fit.  EF-7 and EE-16.

Edit - here's a thread where SteveJ mentions it - http://www.classiczcars.com/forums/topic/47739-73-alternator-upgrade-specifics-with-respect-to-fuel-pump-relay/

@SteveJ

Edited October 3, 2016 by Zed Head

[SteveJ]

34 minutes ago, Zed Head said:

I don't know the details but I think that SteveJ probably does, about how the fuel pump relay is powered from the voltage regulator.  I think the the N pin on the back of the alternator powers the relay so that the pump only runs when the engine is running.  And that small fuse block you show might be the fuel pump fuse, or it might be the one that blew (can't tell which is which is your pictures).  In short, you might have a shorted fuel pump wire or fuel pump relay wire.  Just a guess.  I looked through the FSM and found some things that fit.  EF-7 and EE-16.

Edit - here's a thread where SteveJ mentions it - http://www.classiczcars.com/forums/topic/47739-73-alternator-upgrade-specifics-with-respect-to-fuel-pump-relay/

@SteveJ

That is definitely a possibility. The yellow wire comes off the alternator and is spliced to go to the voltage regulator and to connector C-7 under the dash. From C-7, the yellow wire goes to Electric Fuel Pump Cut Relay #1. Conspicuously absent from this circuit is a fuse. The relays are below the dash on the passenger side near the fuse box. You can find out more about the circuit in the FSM section EF.

[beermanpete]

There must be a short to ground somewhere to melt the wire like that. The bad fuse may or may not be related. Since the fuse opened the wire should have been spared. Follow the burnt wire to the point where it is no longer burnt is about all I can come up with at the moment. Perhaps there is a cut in the insulation at a clamp point or where the wire passed through a hole in the body. The yellow (burnt) wire has about 6 volts on it when the engine is running and goes to the regulator, fuel pump relay (as Zed and Steve said) and the interlock system if it is still there. I don't know what the splice to the white wire is for but it does not look factory to me.

[882993md]

I'm going through the wires from the fuse panel and I found several wires (a green and a black one) from the the fuse panel leading into the engine bay not connected to anything. I'll have to determine where they should go,  or if they are for removed components.

I also found this diagram in the stack of papers showing the voltage regulator connection and the removed interlock.

Howard

 

[beermanpete]

This diagram suggests that the alternator has been upgraded to an internal regulator type. This means the yellow wire is at battery voltage at all times. It is possible that the alternator has failed in a manner that has shorted the "S" terminal to ground. Check for a short from the "S" terminal to ground.

[882993md]

18 hours ago, beermanpete said:

This diagram suggests that the alternator has been upgraded to an internal regulator type. This means the yellow wire is at battery voltage at all times. It is possible that the alternator has failed in a manner that has shorted the "S" terminal to ground. Check for a short from the "S" terminal to ground.

Thank you I will check it.

Howard

[882993md]

Hi everyone:

Happy New Year! It's been a while as been been busy trying to tediously trace wires for opens and shorts. I believe I may have found the issue with the melted S wire.

The yellow wire coming off the alternator and is spliced to go to the voltage regulator and to connector C-7. So I searched for my external voltage regulator and I couldn't find it, so I figured it was internal to the alternator. I opened the alternator and as you can see it has no regulator.

I assume the PO upgraded the wiring in anticipation of an alternator upgrade but never got around to installing the upgraded unit.

The yellow S wire is melted only from the T plug on the alternator to fuse link splice. The wire splice to C7 is perfect condition.

tl;dr No regulator of any kind on S wire