Thanks steve I will try that but could that also be the alt? I know my alt is bad (had it tested) I wonder if that has anything to do with it

  SteveJ said:

You could also be right. I don't know what causes the issue. I don't think that it's because of the presence/absence of an electronic ignition. I have a Crane electronic ignition in my 240 and experienced the run-on.

Anyway, the diode is cheap. It's handy to have in case run-on is an issue.

No, you're right - electronic ignition has nothing to do with it. When I researched this for my own diode, as well as for the plug-in adapter, I found several sources which indicated the diode was necessary only for 240Zs. Some put it the other way, that it wasn't needed for 280Zs. I don't recall any off-hand that actually mentioned 260s, so I'm not certain about them.

As to the reason it's needed - all cars with alternators need a diode. In the old days, generators make DC, which is what our cars use. Alternators on the other hand, make AC, which cycles back and forth. The diode is necessary as part of what converts the AC to DC. Sometimes the diode is within the alternator itself, sometimes it is somewhere else in the electrical system. As best I can determine, in the 240Z system, the diode was inside the alternator. But the ZX alternator doesn't have one in it (ZX's must have had one in the wiring somewhere), so one has to be added.

  Arne said:

No, you're right - electronic ignition has nothing to do with it. When I researched this for my own diode, as well as for the plug-in adapter, I found several sources which indicated the diode was necessary only for 240Zs. Some put it the other way, that it wasn't needed for 280Zs. I don't recall any off-hand that actually mentioned 260s, so I'm not certain about them.

As to the reason it's needed - all cars with alternators need a diode. In the old days, generators make DC, which is what our cars use. Alternators on the other hand, make AC, which cycles back and forth. The diode is necessary as part of what converts the AC to DC. Sometimes the diode is within the alternator itself, sometimes it is somewhere else in the electrical system. As best I can determine, in the 240Z system, the diode was inside the alternator. But the ZX alternator doesn't have one in it (ZX's must have had one in the wiring somewhere), so one has to be added.

Boy, that's a D'oh moment for me. It's been WAY too long since my electrical engineering courses. Maybe I can come up with a better excuse for my brain fart later. Of course, if there is a diode in the charging circuit, I would expect that it would show up in the 260Z & 280Z wiring diagrams unless it's hidden in another component.

I need to start tearing more stuff apart so I can remember how things work.

  mars23z said:

Thanks steve I will try that but could that also be the alt? I know my alt is bad (had it tested) I wonder if that has anything to do with it

Think about the electrical system as a series of pipes. The alternator is analgous to a pump. Corrosion is like putting big rocks inside the pipes. If your pump isn't working, you can't get the water to flow. If there is something blocking the pipe, you can't get the water to flow. So, you may need to clean connections even if you replace the alternator.

As for cleaning connections, a lot of people swear by Craig Deoxit. You can find it online and at Radio Shack.