SteveJ

I posted more about the horns in this thread: I took some video of the work that I need to edit and post on YouTube.

I cracked the code on the horns. I was working on getting @Tirnipgreen's re-plated horns working. I tinkered with them some a while back, but I needed some time to focus on them to get the bugs out. Fortunately I had one of my old 260Z horns that was unmolested to use as a template. Before I go into detail, let's talk about the theory of operation. When you press the horn button, the relay sends voltage to the horn. The coil in the horn is energized, pulling the diaphragm in. The bar on the back side of the diaphragm hits a tab on a set of contacts on the negative side of the coil, de-energizing the coil. The diaphragm snaps back into place, allowing the contacts to close. Repeat steps 2 through 4 as long at the horn button is depressed. The vibration of the diaphragm is what makes the sound. So what appear to be the potential failure points? The tab for the positive wire on the outside of the horn loses electrical contact with the coil inside the horn. The contacts get carboned up. The bar on the diaphragm is not aligned properly. The tone screw is not adjusted properly. I don't have a documented fix for #1. You see it by measuring resistance between the outside tab and the inside of the horn where the coil wire is mounted. Ideally, you should have continuity. For #2, test by measuring resistance from the positive side of the coil to the body of the horn. It should be less than 2 ohms. To lower resistance, I cut a 3/4 inch wide strip of 1000 grit sandpaper and folded it in half. I worked it between the contacts and pulled it through a couple of times, using the tab on the contacts to moderate the pressure. I measured resistance from the positive to body of the horn until it dropped to less than 2 ohms. For #3, I took a straight edge and held it against the side of the bar. There are two alignment holes on the diaphragm, and I noted the distance between the straight edge and the hole. It's between 1 and 2 mm. If the bar on the horn you're working on doesn't line up that close, loosen the M6 nut and rotate the bar. Hold it in place carefully while locking now the nut. After adjusting the internals, put the horn back together. Measure resistance from the positive tab to the mounting bracket of the horn. If it's more than 20 Ohms, the tone screw is turned in too much. The tone screw is an M4 screw on the back of the horn. The screw in the photo below was powder coated onto the horn, and I had to break it loose. I got the resistance from being over 1 MOhm to around 2 ohms. After that I used a car battery to test the horn and get a better tone. I had to work the screw in and out a few times until I was happy with the results. 20230910_153848.mp4 The other horn was a little more challenging. When I tried to break the screw loose, the screwdriver chewed up the head. I had to replace it with the only screws I had available, allen head screws. After playing around with the height of the screw, I finally got a decent volume out of it. 20230910_160521.mp4

I used the roadster belts in both of my Z cars. Yes, the retractor mounts near the quarter window. Here's what you're looking for: https://www.wescoperformance.com/noname.html

I'm actually working on some horns right now, too. I'm shooting video of it, so maybe it will help someone in the future. Anyway, I see 3 main areas for problems. The rivet holding the positive terminal isn't making good electrical contact through the horn body from the tab on the outside to the coil wire. The contacts between the negative side of the coil and the body of the horn are carboned up. I used a strip of 1000 grit sandpaper folded in half, worked it between the contacts, and pulled it through. The bar on the diaphragm that opens the contacts isn't adjusted properly, so it doesn't open the contacts. You call tell this in a test if you feel the diaphragm pull in when you apply voltage to the horn.

The extractor kit I linked goes inside what's left if there is a hole in it.

Of course, that would explain fuel pump issues.

Do you mean like this? https://www.vintageconnections.com/products/6-3mm-connectors?variant=46131501236545

One thing I'd like to add, @Patcon & @grannyknot, Consider getting a DPDT switch like this: https://www.amazon.com/Heavy-Handle-Momentary-Toggle-Switch/dp/B000LFVFA8 You can wire the LW, LY, L, & battery negative wires to the switch. Battery negative goes to the center posts on either side of the switch. LW gets wired to one pole on each side of the switch. L gets wired to one side, and LY gets wired to the other side. You might want to mount the switch to something because the terminals might get warm. Also don't forget to fuse the positive at 20A and use 14AWG minimum.

If you're near a Harbor Freight, you could get these: https://www.harborfreight.com/screw-extractor-and-left-hand-drill-bit-combo-set-10-piece-63987.html https://www.harborfreight.com/3-piece-t-handle-tap-wrenches-38560.html Also 25% off coupon that's good today and tomorrow: (https://www.harborfreight.com/promotions) BTW the coupon will work for jack stands. I wanted to get a set of 6 ton stands, so it worked for about $20 off today.

Take a photo of what's sticking out and post it here.

Sure, but you'll probably need a car battery or heavy duty power supply to make that work. LR - 12VDC+ B - 12VDC- Low - Connect L & LW to 12VDC- High - Connect LY & LW to 12VDC-

Well, I searched more. They have 9 & 11 mm, too. https://www.authenticclassics.com/SearchResults.asp?Search=cloth+braided+type+fuel+hose

2? 4? What difference does it make?

And this place has 9 & 11 mm ID https://www.autohausaz.com/catalog?k=braided+&b=&page=1&sortby=r

Here's some, but at a much higher price. https://www.authenticclassics.com/Mercedes-Cloth-Braided-type-Fuel-Hose-8mm-I-D-p/auth-008783.htm

Many different sizes are available from Belmetric. https://belmetric.com/hose/gasoline/

I actually happened across some of your posts there when I was doing research on EDIS with Megajolt today.

I don't recall ever seeing security screws on the ignition switch module, and that includes 2 new Beck Arnley full switches that had Nissan part numbers on them. (I never knew Beck Arnley was a Nissan supplier until I bought them.) On the other hand while it's security via obscurity, it is not a trivial task to get to those screws. It would be a determined thief doing that, and at that point he's going to take your car pretty much any way he can. I have replaced the ignition switch module on a car just as I described. It helps to have a stubby screwdriver or a mini ratcheting bit set like pictured below.

Yes, the vertical is for the fuel pump, and the top of the T is for the gauge.

Yes, you can use battery negative for ground. (Also, if you look through my YouTube channel, you'll see a video where I show how to check the quality of your grounding. Bad grounding can cause some perplexing problems.) Yes, you can check the functionality of the sensor. You measure resistance to ground at the top of the T at the sending unit. Remove the connector from the sending unit. Get your baseline resistance reading between the top of the T and ground. It should show very high resistance. You will need to ground the pin on the connector that connects to the fuel pump relay so you get fuel to run the car. Have someone start the car while you continuously measure resistance to ground at the sending unit. Resistance should drop.

Yes, the oil pressure sending unit was changed for 78. In previous 280Zs, the flap in the AFM would close a switch to tell the fuel pump relay that the engine is running and kept power on the fuel pump. Nissan moves away from that Bosch fuel pump relay and used oil pressure as a signal that the engine is running. If you look at the 75-77 wiring diagrams, you see terminal numbers 36 and 39 on the AFM flap. This is how they documented the change on the 78 wiring diagram. So, yes, the oil pressure sender grounds when the engine is running on the vertical of the T. That circuit is for when the key is in ON.

You can actually test to see if the gauge is functioning properly. There is a T shaped 2 pin connector on the oil pressure sender. The top of the T is the wire that connects to your gauge. You want to measure voltage to ground on that wire with the key in ON. At first, you should see full voltage, then it should start to fluctuate. A while back @Captain Obvious gave a great description of how it worked, and I bought an analog ammeter to demonstrate it. Since voltage and current are proportional, you'll see the voltage reading start to dance after the gauge warms up. Keep in mind that the oil pressure gauge and temperature gauge use the same voltage regulator, so if you don't see the voltage start to dance when you are checking the wire at the oil pressure sender, you can do the same test at the wire for the temperature sender. If one works, and the other doesn't, my first guess would be that there could be a wiring issue or corrosion at the dash to engine harness connection. Anyway, do this test and report back, and we can figure out if more diagnostics are needed.

Not needed if you only get the back part. You can get to the screws on the back using the instructions I posted.

Could it be the module on the back of the switch? Yep. It could, and I know from helping other people that the symptoms can make it look like a bad ignition relay. The nice thing is that you can replace the back of the switch with an OEM part. The part number is 48750-E7705. You can try Courtesyparts.com or Nissanpartsdeal.com. Either site is reliable. To replace: Disconnect the negative battery cable. Remove the cover from the steering wheel. Unplug the connectors from the combo switch and ignition switch. You may want to label them for faster reassembly. Remove the 4 bolts under the steering column that holds it to the dash. Push down on the steering column so you can access the screws on the back of the ignition switch and remove the old switch. Install the new switch and reverse the disassembly process. Curse under your breath if you didn't follow my suggestion in step 3. Re-attach the negative cable and test.

The brake warning lamp is on the same fuse as the turn signals. You already established you have low voltage at the fuel gauge fuse. You probably have the same low voltage at the turn signal fuse. The voltage is enough for the light to come on faintly, but it's not enough to trigger the flashers to flash or get the gauges to operate.