SteveJ

Good. I know sometimes technical information doesn't translate well. Here are a couple of photos. The wire for the horn is attached to the ring at the same point where I drew the arrow in your photo. Looking at your picture, it looks like you are missing a couple of the insulating washers that go under the metal washers.

Is my information translating well for you? If not @dutchzcarguy could probably explain it in Dutch.

The black wire should connect to the ring. The ring should not be grounded until the horn button pushes the ring against the steering column. In the attached video, you can hear the horn relay click as I push the ring down into the steering column. Horn button movement.mp4

What you are finding is normal. Here is a simplified view of the circuit. When that black wire is not in contact with ground, it will show 12 volts to ground. From the positive on the battery to that point, the circuit acts as one long piece of wire. That is what is in the red cloud. Once the black wire comes into contact with ground, the coil in the horn relay is energized and will act as a load.

The ring where the wire mounts should not be grounded all of the time. When you press the horn button, the ring makes contact with the steering column that is grounded. What is wrong with your horn is that wire is mounted to one of the 3 screws that holds the ring to the steering column. The mounting screws have insulators to isolate the ring from the steering column. The wire should be connected at the empty hole, and there should be an insulating washer at the screw where the horn wire is currently mounted.

Yep, especially when someone in Alpharetta (near @inline6 ) posted an 83 5-speed that wasn't even cleaned up for $700.

I let a couple of friends in the area know about this in case they know of someone looking for a 5 speed.

Considering that most people re-wire the fuel pump with little regard for safety, I would restore it to stock. It's not as safe as having an inertia switch, but at least it will cut off the fuel pump if the engine stops running.

I see some corrosion, but for a car that's about 50 years old, that's not unusual.

What do you know? Another thing on my roundtuit list that I completely forgot about. Thanks for following up with Shawn.

Thank you, Shawn. @The Unobtainium

That is the EFI fusible link. I can't talk to one side being plastic, though.

I also forgot to mention, you should hear a click when going to ACC.

Be careful. There are two relay coils, and hearing a relay click doesn't mean the contacts are good. Check the fusebox for voltage where I indicated to verify. (Note: Ideally you want to load test as the presence of voltage does not mean the circuit can handle current, but it's good enough to test for voltage right now.)

If you find that the ignition relay has given up the ghost, you can make your own replacement with easily acquired parts or buy them already assembled from ZCarDepot. https://zcardepot.com/products/starter-relay-upgrade-replacement-280z?_pos=1&_sid=fb635bdb1&_ss=r

Many circuits in the fuse box get power from the ignition relay. Are you sure that relay is functional? It is found on the passenger kick panel. Since it is mounted upside down, it is prone to water infiltration/corrosion over the years. The fuses in the red box only have power with the key in ON and ignition relay functioning. The fuses in the green box only have power with the key in ACC or ON and the ignition relay functioning.

I knew I could count on you, @Captain Obvious

I suggest using a marine type maxi fuse holder. Littelfuse makes a line that I believe would work well. It's the Maxi 152 series. https://www.littelfuse.com/products/fuses-overcurrent-protection/fuse-holders-fuse-blocks-accessories/fuse-holders/in-line-fuse-holders/maxi-152 I am thinking it would be a part number like 01520005Z. I attached the cutsheet from Littelfuse. Littelfuse-MAXI-152-Series-Datasheet.pdf To crimp the terminals properly, you would need a set of crimpers like this: https://www.amazon.com/dp/B0978S514B Are you sure the voltage regulator has been jumpered out? You can verify with a multimeter. Measure voltage to ground on the yellow wire at the T plug on the back of the alternator. If it has voltage, the regulator has been jumpered out. However, if that's the case, it would cause problems when the car is running, like human sacrifice, dogs and cats living together... MASS HYSTERIA! Okay, maybe not that bad, but you get the picture.

Is that at a Publix? If not, @Yarb will never see it.

And don't forget that if you need to resort to a 4-speed bell housing, I have one just up the road from you. You just get stuck with the broken transmission attached to that bell housing. 😁

If you disconnect the tach, and the car runs, it would mean that the tach isn't in the ignition circuit. The other things to check are the power and ground to the tach in the dashboard.

That, I can't answer for you.

If fuel is actually leaking from the damper, it's probably toast. Fortunately, there is an aftermarket replacement. https://zcardepot.com/products/fule-injection-pressure-pulse-damper-efi-280z-280zx

If you disconnect the tach, does the car still run?

The first thing I have to ask: Did you verify you have voltage at the horn when you press the horn button? I had to deal with a fair amount of corrosion on the horn tab in my 73. Also, do you hear the horn relay click?