SteveJ

Also, where did you mount the electric fuel pump, and what is the orientation? What does the manufacturer's installation instructions say? What brand/model electric pump did you install?

Make sure your fuel filter (stock design) is mounted vertically with the outlet on top. Inside the fuel filter, the opening for the outlet is low when the filter is mounted properly, so the fuel does not fill the filter typically. I hope this image give you a good visual. The photos you posted are in a format that users with Windows computers cannot open easily. I am lazy and do not care to install software that allows me to look at them. You may want to look at converting the photos to a JPG format. As for fuel starving, go back and give us details. Why did you add in the electric fuel pump? Do all of the fuel lines have smooth bends that don't kink the hoses? Have you checked the fuel pressure between the pumps? You don't want too much pressure (>4 PSI) on the fuel rail, as you will overwhelm the floats.

Absolutely...NOT. As I said in my first response, you don't have an oil pressure switch in your car. The sending unit only supplies a signal to the gauge. The sending unit should have resistance with the engine off. EFI relay and fuel pump operation in more detail: The W/B wire (from the Ignition Relay) brings 12VDC to the EFI relay coil 1 on pin 71. The W/B wire has 12VDC when the key is in the ON position. At start, the B/Y wire from the starter brings 12VDC to the EFI relay coil 2 on pin 76. (and it is supplying 12VDC to the cold start valve via pin 47) It is also sending voltage to the ECU from pin 20. Pin 72 is the ground signal for both coils. It is grounded through the ECU. At start, the EFI relay coil 2 closes the contact between pins 73 and 74 when the ECU grounds pin 72. Pin 73 gets 12VDC from the W/R wire that comes off one of the fusible links. Pin 74 is the G/L wire going out to the gas tank. When pin 72 is grounded (Key in ON), 12VDC from the W/R wire at pin 70 (from the EFI fusible link) is connected to pins 39, 10, and 43. When the AFM flap is open, voltage goes from pin 39 to pin 36. This allows pin 36 to energize the EFI relay coil 2. The contact closes between pins 73 and 74, sending voltage to the fuel pump. Since you said you aren't getting voltage to the fuel pump (and you have a good ground at the fuel pump), I am thinking the ECU is not providing the ground for the EFI relay like it is designed to do. Another alternative is that you have a bad/missing fusible link for the EFI. This fusible link is sometimes overlooked because it is not mounted on a nice block like the other four. (See the last response in this thread: https://www.zcar.com/threads/where-is-the-darn-fusible-link-for-the-fuel-injection.278457/) With everything connected, make sure you have 12VDC to ground at pin 70 on the EFI relay. Make sure you have clean connections between the ECU and wiring harness. Also make sure the ECU is grounded where it needs to be grounded. You will likely need to go through the ECU diagnostics as described in the EF section of the 77 FSM if you have 12VDC to ground at pin 70. If you haven't done so already, download a copy of the FSM. You can find it here: https://www.classiczcars.com/files/category/13-280z/

Actually there is no oil pressure switch for 75-77. What @240zadmire doesn't say is whether or not he moved the AFM flap. When the key is in the ON position, the fuel pump doesn't run when the flap is closed.

I found a forum thread for Honda motorcycles where someone was replacing a thermistor. (https://www.electronicspoint.com/forums/threads/thermistor-in-a-gas-tank.123318/) The suggested replacement thermistor is from Amphenol, RL2004-582-97-T10. That part does not come up, but this one does: RL2004-582-97-D1. It's only 1K Ohm.

At least I know I'm not going to be the only one from ClassicZCars at ZCON.

Here you go, @Captain Obvious. I uploaded @Yarb's video to YouTube. https://youtu.be/uQcu71wOkpw

Probably, try to disconnect the sensor under the passenger seat.

As long as it's not cancelled, I will be there.

So I did some ZCON prep today. When I replaced the fuel sending unit few years back, I put new terminals on the wires at the sending unit. It worked fine until recently when I lost the signal. I needed to rotate the tires, so with the car on the lift, I figured I would check out the sending unit. The terminals were loose. I used the type terminals found on the connectors used throughout the car, but they are a fraction of an inch too large for the sending unit terminals. I tried a female spade lug, and it fit snug on the sending unit, so I replaced the terminals again. My fuel gauge has a good signal, and my tires are rotated. Next up, I want to do another headlight experiment, and the car should be ready for the road trip.

Did you ever bleed the MC?

The fuel warning light works via resistance dropping at the thermistor in the gas tank as the thermistor heats up. There is not another wire on the negative leg that could complete the circuit during engine start.

You merely joined the long list of us that have made that mistake or one like it. I think I made that one in 2008.

From the 72 FSM, but I don't think it's different from the 71: I hope to assume that the actual reading you had on the secondary was 8.95K Ohms. Based upon that assumption, if you have everything wired correctly, you should have no problems. What is prompting your question?

@26th-Z This is all I could find that seemed relevant: By the way, @Mike, I really like the search features of the software running this site.

I suggest posting photos and taking measurements. There are several members of this site that have an oil pan they could compare your findings to.

Automotive bulbs are rated for 14 VDC. (sometimes 14.4) https://www.bulbtown.com/9428049_GM_General_Motors_Replacement_Bulb_p/9428049.htm https://www.bulbtown.com/274020_GM_General_Motors_Replacement_Bulb_p/274020.htm https://www.bulbtown.com/1813_Miniature_Bulb_Ba9S_Base_p/1813.htm https://www.bulbtown.com/274004_GM_General_Motors_Replacement_Bulb_p/274004.htm https://www.bulbtown.com/363_Miniature_Bulb_Ba9s_Base_p/b363.htm There are probably others within that list. I didn't go down each page.

It wouldn't surprise me if it's an "off-the-shelf" piece that was used in creating the reproduction sending unit. And by "off-the-shelf" I mean that it is designed for a more recent car/electrical system, maybe even for LED lights. That would explain why the light comes on so soon for the incandescent bulbs. Unless ZCarDepot has someone as thorough as the good Captain when specifying the behavior for the reproduction, a thermistor with the wrong curve could have been used.

The Fry's closest to me (about 3 miles from my office) was almost an empty warehouse the last time I visited. Are they back to stocking products?

A pot runs a few dollars (plus shipping since Radio Shack is no more). Low wattage BA9 bulbs were pretty cheap at the link I posted. You would need no more than a 100 Ohm rating on the pot, and then you have to modify the wiring to incorporate it.

@Captain Obvious, do you mean like this? So it seems like the thermistor isn't spec'd correctly from the experiments run by @dmorales-bello. As @Dave WM said, a lower wattage bulb would be higher resistance in the line. In theory you could use a potentiometer to adjust the resistance, but it would be cheaper just to try a lower wattage bulb to see if that's a viable workaround.

If you want to experiment further, here is a site with different wattage bulbs: https://www.bulbtown.com/9mm_Diameter_Bayonet_Base_s/1421.htm

Wattage is proportional to current. It is also proportional to voltage.

I was wondering about the bulb wattage, too, based upon one of the links I posted. So @dmorales-bello, are you game to try a different bulb?

See, now you made me go look. The FSM doesn't have much in the FE section, and the BE section refers to the FE section. I asked my frenemy Google about this and found a couple of interesting threads in other forums. https://www.element14.com/community/thread/56806/l/which-thermister?displayFullThread=true https://advrider.com/f/threads/honda-thermistor-fuel-light-to-led.954021/ As was mentioned earlier, the wattage of the bulb and characteristics of the thermistor come in to play. (Thanks for the re-hash, Steve. Do you have anything to add to the conversation?) I tried a search to see if one could buy a fuel light thermistor. Sure enough, there are some listings on ebay for some Chinesium thermistors. I'm not sure I would want to experiment with incorporating one into an existing fuel sending unit. https://www.ebay.com/itm/Automotive-Fuel-Level-Sensor-Fuel-Pump-Alarm-Sensor-NTC-Thermistor-/283606453547?_trksid=p2385738.m4383.l4275.c10