SteveJ

You may want to look for Aisin water pumps. I saw some on ebay and CardID The issue might be whether or not you need a pump with a fan clutch. Those are rare. I just noticed that the Aisin is available via Rockauto but I had to click a button to unhide it.

The rule of thumb is 10 PSI/1000 RPM. Full scale is to 90 your car, so 10 PSI isn't that far up the scale.

I'm pretty sure it was on there when I bought the car 30 years ago. It seems to work fine.

Lord knows how long this sender has been on this car...

That was a cigarette lighter USB power adapter. You can find those on Amazon all day long. https://www.amazon.com/gp/product/B01M9IKYVH It's just measuring the voltage at the cigarette lighter. That should be the same voltage as the battery/alternator. It has no interaction with the ammeter. The only caveat about that modification is that it will affect the stock wiring for the fuel pump since you will not have a neutral wire from the alternator. If you have rewired the fuel pump circuit, then it's no problem. When I did the fuel injection on my 260Z, I no longer controlled the fuel pump with the neutral from the alternator, so it was a no-brainer for me.

https://www.carpartsmanual.com/datsun/Z-1969-1978/electrical/electric-unit-switch/section-1/240z-260z Part 34 https://www.nissanpartsdeal.com/parts/nissan-ol-pres-gaug~25070-89901.html

If said you saw a voltmeter in that video I linked, you need to go look again. I never installed a voltmeter in my car.

Well, since you're not concerned about stock...

It's in my neck of the woods, too.

Yep, I was pretty sure he would be replacing the sending unit with that much difference.

I would say the resistance reading is higher than I would expect. At least now you know you aren't just throwing parts at the problem.

What scale did you have your meter set on?

It's easy to f#@k up an AFM.

Another 1st Sunday of the month with great weather meant the Zs showed up again.

It was too windy yesterday for me to sit and let the car come up to temperature. I was driving it today, so I did before and after photos. The interesting thing is the narrow band in resistance between stone cold and operating temperature. Cold: Operating temperature (from a very nice drive today)

That's to drain off the extra electrons so they don't fill up the starter.

I can probably shoot a demonstration video of the sender tomorrow to give you something to compare readings to. I believe you're familiar with my YouTube channel.

That sounds like an intermittent connection. On my 240Z I thought I had a sender going bad. I replaced it, and the gauge registered for a little while before it stopped working again. I checked the connector, and it was just barely attached to the wire. I put on a new female bullet, and I've had no problems since. Did you take a resistance measurement from the sending unit to ground like I suggested?

A diode won't help you. Here's the issue: something is limiting current flow, such as a dirty fusible link, corrosion at the ignition switch, or poor contacts in the ignition switch. What ever the cause, the limits on the current flow result in lower voltage in the ignition circuit. Think if a partially blocked pipe. Water can still flow through it, but as you open more valves downstream of the blockage, the pressure (voltage) drops. If you put the year of your car in your posts (or in your signature), I can give specific diagnostics. There's a good chance one of your future best friends will be a Dremel with a wire brush to knock off corrosion.

You didn't use the ignition circuit to power the fan, did you?

The thermostat has a weep hole for some coolant to pass before the t-stat opens. Here's the 280Z t-stat housing. This drawing shows the EFI sensors and switch. I think I found what you are referring to. Here are most of the part numbers in that drawing: No, I didn't see any mention of this in the 75, 76, or 78 FSM.

There is no coolant bypass. When the watercock valve is closed, it is deadheaded.

It's just for the "key in" buzzer. I'm not sure what all you would have to disassemble to get to where it goes.

Someone reported these as being dimmable. I can't remember if it was @cgsheen1 https://www.amazon.com/gp/product/B0B9MGSX7K Update: It was @kully 560 who used them.

I'm up in the northeast corner of Forsyth County near Lake Lanier.