1973 240Z Horn signal wiring/relay location

[hotsho111]

Thanks @cgsheen1, that's what I initially thought. I can't confirm if the frame ground is intact but I would assume so.

I know it was common to ground columns around that time via the rag joint for the steering column so I was going to look into that next. The rag joint parts and the column are painted so I was gonna check if something wasn't able to ground because of that.  

Another question I've had some trouble trying to confirm looking at the wiring diagrams: should the red/black wire that connects to the brass arm that touches the steering wheel have 12v power or should that be purely ground? 

Mine has 12v so when I press the horn button (grounding the "column" via the ignition switch bracket) I get a small spark which makes sense in that context, but I would have thought that would all just be a ground circuit with no power

[SteveJ]

48 minutes ago, hotsho111 said:

Thanks @cgsheen1, that's what I initially thought. I can't confirm if the frame ground is intact but I would assume so.

I know it was common to ground columns around that time via the rag joint for the steering column so I was going to look into that next. The rag joint parts and the column are painted so I was gonna check if something wasn't able to ground because of that.  

Another question I've had some trouble trying to confirm looking at the wiring diagrams: should the red/black wire that connects to the brass arm that touches the steering wheel have 12v power or should that be purely ground? 

Mine has 12v so when I press the horn button (grounding the "column" via the ignition switch bracket) I get a small spark which makes sense in that context, but I would have thought that would all just be a ground circuit with no power

You're just not thinking about electricity the right way.

Another term for voltage is potential because you have potential (aka stored) energy when the circuit is not complete.

Here's a rough diagram of the horn circuit.

You go from the positive of the battery to a fuse (not shown) to the horn relay. The electromagnet in the relay is just a long piece of wire. When the horn button is not depressed, there is no current flowing through the wire of the engine harness, dash harness, or horn relay. So you have a long piece of wire attached to the positive terminal of the battery, and that wire includes the red/black wire going to the horn button. Measuring along any point of that wire is the same as measuring at the positive terminal of the battery. The red/black is not at the ground state.

When you press the horn button, you are putting the red/black wire at the ground state with the negative terminal of the battery. Now you have current flowing. The electromagnet in the relay is pulling in the contact to sound the horns. You're going from potential energy to kinetic energy because work is being done. 

So until you press the horn button, you should see voltage to ground at the green/red wire.

[SteveJ]

So I went out to check to see where exactly is the best point to measure ground on the steering column. For the body ground, you can use one of the screws on the scuff plates in the doorframe. Here is where you should put the other probe on the steering column. Be sure not to touch the top ring.

As for the body ground, it's in the engine bay. Unless you have a host of electrical issues with your car, the ground should be there. I put a battery cable from the negative to the grounding point because I could. It's on the passenger side of the engine bay, not too far from the firewall.

 

[hotsho111]

Thanks for the explanation @SteveJ, I'd been doing some research today and went over something similar with a buddy so it makes more sense now.

Thanks for the ground check spots. I can try checking that tomorrow.

[hotsho111]

Finally had a chance to get to this today. The ground strap is there but it's connected to the starter starter but there are a few small ancillary grounds that do go to the body.

@SteveJ I tried checking for continuity from the spots you indicated on the column and no bueno. 

I'm not sure if the column ground is supposed to come from where it's bolted to the firewall, the metal bulkhead, or from the steering coupler in the engine bay. I thought the columns were generally grounded through the steering coupler joint as the column was generally isolated from the column tube. I'll have a little more time tomorrow and might start poking at that

[SteveJ]

That should work for body grounding. I did a regular cable because I am me.

Check for resistance from the negative battery terminal to the bolts on the passenger side shock tower. It should be close to 0. If it's more than a couple of tenths, then something is wrong with your technique, or there is something wrong with the grounding.

Has anything been refurbished or refreshed around the steering column. Sometimes when people try to make things pretty, the paint they used insulates a part from ground.

 

[hotsho111]

Taking that resistance reading with the ignition in the lock position it reads .2 ohms. With the key in the ACC position it reads about 8 ohms

The car was restored in ~2010 and they painted a lot (which is why I've been trying to track down what should be the source of ground).

I was poking at the steering coupler and the column does have continuity through the coupler but it doesn't have continuity to the input shaft to the steering box (that does have ground though). I'd guess it's because a bunch of this stuff has been painted over

I've attached a picture to try and help. The red circled bolts have continuity with the steering column. The green part has continuity to ground. I think there should be a connection between the two where the steering box input shaft is bolted to the H section of the coupler. The H plates have been painted blue so I'd guess that's why there's no continuity there.

I think the "proper" solution is to probably take those coupler plates off and make sure there's not paint preventing contact, but the easier solution (and what I'll probably do) is just buy a short grounding strap and connect them that way

[Captain Obvious]

I have very little 240 experience, but I wouldn't expect the steering coupler to be the "planned" source to ground the steering column.

I would expect the steering column to be grounded through the bolts that hold it to the firewall or the bolts that hold it up to the underside of the dash.

[hotsho111]

I definitely thought the same thing but it looks like that coupler is a pretty common ground approach for 60s/70s vehicles (American ones at least). The column might get ground from where it's bolted to the firewall as it looks like the steering column bearings aren't rubber coated like some other steering columns from the period so there should be some contact there

I know the entire column is isolated from the dash mounting bracket as that mount has a rubber gasket so it shouldn't touch the column housing

[Captain Obvious]

So I (actually) read through the details of the thread this time and I think I have a better understanding of what's going on...

The issue you are having is that the steering SHAFT that runs through the center of the steering column assembly does not seem to be grounded. The outer shell may be (or may not be), but that isn't good enough to get the horn the actuate. You actually need the rotating steering shaft in the center to be grounded.

So, I agree though... I would expect the center shaft to get grounded through the roller bearings, but maybe not?

Have you tried grounding the outer tube with a dedicated wire and seeing if that makes your horn work?

 

 

 

[hotsho111]

I connected a ground strap to the ignition switch and that grounded the column and the horn worked then (which is how I ID'ed it being a grounding issue).

I also agree in that I'd expect the center shaft to be grounded via the bearings since they are metal. American cars of the period would use a metal bearing in a rubber sleeve so it makes sense why those needed a grounding strap. I don't know if the housing was painted or what as it doesn't seem to be grounded through the housing

[SteveJ]

Well, I can't explain why your steering column wasn't grounded well enough but, but it sure sounds like you solved the problem.