Voltage Regulator Question

[503Alex]

I had a bad regulator on my '77 (bouncing volt gauge) and ended up buying a new one off of BD. Oddly enough when I took the old one out, one of the wires from the 6 connector was not soldered to the regulator and was cut short. I though that was odd, so I jumpered that wire and it sounded like it may have been the cold start injector, although I am unsure.

I received the new regulator from BD and installed it today. When it got power, the regulator let out a bug puff of smoke. Turns out that the wire that burned out was the same wire that was cut short and not soldered on the previous regulator. The good news is that the gauge is steady now at the appropriate voltage (for now at least).

Any idea what the disconnected wire in this picture that burned out goes to? (black wire) It is cut off so it doesn't become a fire hazard. I need to figure out what the electrical issue is before I reconnected/re-solder that connection. I've looked through the wiring diagrams in the FSM pretty extensively but haven't found it.

Thanks in advance for the help!

[SteveJ]

My guess is that it's the ground since it's the only black wire on the VR.

I'm attaching a picture from the 76 FSM. The wiring should be the same on a 77. Match it up to the plug on the wiring harness side. The top of the VR plug lines up with the bottom of the wiring harness plug. The letters on the VR side will tell you the function.

If you don't know what the function is, post the letter going to the VR.

[sblake01]

My guess would also be ground since there doesn't appear to be anything insulating that solder joint from the body of the regulator.

[FastWoman]

Yeah, looks like a ground point on the VR. The good news is that you wouldn't have damaged your new VR or any component of the charging system. You might need to reattach a black wire to run to ground, BUT...

The black wire that burnt is apparently NOT a ground. It would have to be hot to burn when connected to a ground point. You've got something wired wrong. I suppose the ground wire would be redundant with a simple mechanical grounding of the VR to the chassis. I suspect the purpose of the wire is to make CERTAIN the VR is grounded, so as to avoid an overvoltage that might damage sensitive electronic systems. So I think it might be good to figure out the right ground.

[503Alex]

Thanks for the help. The wire that burnt out is the #6 on the voltage regulator connector (to the left of the top on the connector) and #2 on the harness connector.

I also found this link (http://www.atlanticz.ca/zclub/techtips/alternatorswap/index.html) which seems to shed some light on the differences in wiring between the years, and from what it looks like, it's the "A" wire on the '77.

Edited February 16, 2011 by 503Alex

[SteveJ]

Thanks for the help. The wire that burnt out is the #6 on the voltage regulator connector (to the left of the top on the connector) and #2 on the harness connector.

I also found this link which seems to shed some light on the differences in wiring between the years, and from what it looks like, it's the "A" wire on the '77.

Alex, I'm confused by your response. Pins #6 and #2 don't connect. They are separate wires. The attached picture shows the pin numbers on the VR connector, too.

By the way, do you have a voltmeter (not the gauge in the car) to see how much voltage you read at the battery with the car running at 2500 RPM?

Steve

[503Alex]

Alex, I'm confused by your response. Pins #6 and #2 don't connect. They are separate wires. The attached picture shows the pin numbers on the VR connector, too.

By the way, do you have a voltmeter (not the gauge in the car) to see how much voltage you read at the battery with the car running at 2500 RPM?

Steve

Steve, thanks for the clarification, for some reason I misinterpreted the picture and though that the VR connector and harness connector were numbered differently. It's definitely the #2 pin then. I have a voltmeter to check that with.

Edited February 16, 2011 by 503Alex

[SteveJ]

Something isn't right. If you had it such that the black wire on the VR went to pin #2, I'm not surprised it burned to a crisp.

In DC wiring, black is typically used on ground wires, hence the first posts from me and Stephen. If someone managed to install the VR without lining up the pins properly, and the black wire on the VR ended up on pin #2 of the engine bay connector, it would burn up quickly because it's a dead short.

With the battery disconnected, try the plug such that the black wire on the VR lines up with pin #4 on the engine bay plug. See if it plugs in that way.

[503Alex]

Yeah, it is quite odd. I went and confirmed that the only way is plug it in is the way that I had it due to the directional plug. I think what happened is the manufacturer of the new VR decided to not use the same color wires as the harness uses. I checked and the wire that the black/white wire that fired is connected to is indeed the white/red (A) wire in the diagram.

[503Alex]

Is it possible the VR was improperly wired? Although it does seem odd that the same wired that fried was cut short on my previous VR and not soldered, and that the new VR works fine.

[SteveJ]

At this point, I don't have a 280Z to verify wiring on the harness or VR. If you notice in your picture, the terminals for the other 5 wires are insulated from the case. The one that smoked was not. Combined with the wire color being black makes me pretty sure that it's a ground wire. I'm not sure how you could be charging your car without something connecting the VR to the white/red wire.

This leaves you with three options.

1. Hope this never causes you problems.

2. Wait until someone with a 75-78 280Z can verify anything on this thread.

3. Swap to an internally regulated alternator following the guide on Blue's website.

[Zed Head]

E represents Earth or Ground. If you have a voltmeter, you could see if Pin 4 on the harness connector has power when you turn on the key or is grounded, key off. According to the diagrams, it should be a ground wire.

What you've described so far is as if the wire to pin 4 from the harness has power to it when the key is turned on. It's possible that someone had a short in the past and the wires melted together in the harness, or that insulation has frayed away over time inside the bundle.

If you connect your voltmeter positive to Pin 4 from the harness, and the voltmeter negative to ground, then get power when the key is turned on, there is a short somewhere along the Pin 4 circuit. It might be burned at the other end also.

My 76 has some wires stuck together in the main harness from a short sometimes in it's past (before I got it). The ground wires run right alongside the power wires in the harness. The ground wire got hot and almost took the whole harness out.

Edit - my clairvoyance is acting up again...

Edited February 17, 2011 by Zed Head