Had an odd problem today with some wiring

[alloy]

On my 55 I had to replace the horns and picked up a nice set from the local pick and pull. I got them mounted and wired up and they wouldn't work. I checked the horns before leaving the wrecking yard by jumping them on my car battery so I knew they were good

The horns have good 12v power to them. They are mounted right beside my transmission cooler fan. I tee'd into the ground wire of the fan and ran it to the engine block. I'm a really big fan of having a good ground so that's why I ran it to the block and not the core support.

At first I thought it was my horn relay that was bad so I replaced it. When I put the new relay in the horns kind of made a wimpy little sound and that was it. So I jumped the relay ground so it was on all the time and went to the front of the car and my trans cooler fan was on, but the ignition was off and the fan thermostat was not triggered. So I took the ground off the relay and it stopped. Jumped it again and the fan came back on, but was turning backward.

So I cut the horn ground wire at the t and the fan stopped. So I took a jumper wire and ran the horn ground directly to the engine block and the horns work., fan was still off.

The only thing I can figure is by sharing and teeing the ground with the fan somehow the power to the horns were diverted to the fan and the fan motor sucked up all the power from the horns somehow.

Am I right on this?

 

[GoceKU]

Some horns have a little resistor to ground, for self diagnosis. If you've switch the wires put the positive to negative could cause the widnes you've mention. I've changed horn on a GM, the new horn works but is showing message that is defective, so i had to put the factory horn and run rely to the new ones.

 

[Jake M]

On my 55 I had to replace the horns and picked up a nice set from the local pick and pull. I got them mounted and wired up and they wouldn't work. I checked the horns before leaving the wrecking yard by jumping them on my car battery so I knew they were good

The horns have good 12v power to them. They are mounted right beside my transmission cooler fan. I tee'd into the ground wire of the fan and ran it to the engine block. I'm a really big fan of having a good ground so that's why I ran it to the block and not the core support.

At first I thought it was my horn relay that was bad so I replaced it. When I put the new relay in the horns kind of made a wimpy little sound and that was it. So I jumped the relay ground so it was on all the time and went to the front of the car and my trans cooler fan was on, but the ignition was off and the fan thermostat was not triggered. So I took the ground off the relay and it stopped. Jumped it again and the fan came back on, but was turning backward.

So I cut the horn ground wire at the t and the fan stopped. So I took a jumper wire and ran the horn ground directly to the engine block and the horns work., fan was still off.

The only thing I can figure is by sharing and teeing the ground with the fan somehow the power to the horns were diverted to the fan and the fan motor sucked up all the power from the horns somehow.

Am I right on this?

I've got no idea how it's wired (all of everything even closely related) to give you exact specifics, but that screams of a bad ground circuit. You "shared" a ground with another component, now the original component (the horns) show symptoms of low voltage. And the other component (the fan) shows signs of having voltage. Current is clearly flowing through both of them. That would put the two of them in a series circuit, which is exactly what would happen if that shared ground weren't grounding properly. Activate the horns, let the cooler fan run, attach your volt meter ground lead (NOT test light) to the battery negative post, and see what the voltage is on "T" wire ground circuit. If you've got much of any voltage, move from accessible point to accessable point. Maybe the T in the wire, to the engine block bolt, the block it's self, the battery/fender/frame ground, wherever that return path to the battery negative post leads you. When you find a place where the unexpected voltage goes away, you've found the section of the circuit where there's resistance and/or an open circuit, you can narrow your search to that section between the failed test (voltage where there shouldn't be much of any) and the first passed test (ground potential on something that should be ground).

 

[pdentrem]

Do you have a ground strap from the chassis to engine block? Body to block or chassis? Naturally you have one from engine to battery otherwise not much would be working.

 

[markba633csi]

Grounding issue, yep sounds like

 

[ddillman]

Most older cars had 12 volts to the horn and then grounded through the horn button on the steering column

 

[alloy]

Yes I have a ground strap from the engine to the block but I don't have anything grounded to the chassis or the body. The negative battery cable runs from the trunk to the engine block on one of the transmission bell housing bolts. I do have a grounding block that is attached to the engine block with a 8awg wire for the small things. The horns are the only thing I had a problem with.

I'm kind of anal with grounds. When I did the LS3 swap in my nova I bought the extra ground kit. The tech with the company that made the swap wiring harness for the LS engine told me that 95% of the problems they have had has been traced to a bad ground. I remembered that when I put the new harness in the 55. And AAW (american autowire) that supplied the ugrade wiring harness also mentioned ground problems with customers. I also realized that the car is 68 years old and has seen a lot of miles and just because I ground the body at one point doesn't mean the entire body is grounded. And since the battery is in the trunk it was very easy to run a ground wire from the tail lights to the negative battery terminal. My lights are very bright this way.

Yes the horn relay is activated through the horn button. The only thing I can't really figure out where the ground comes from is the steering column shaft. I don't really see a clear path to ground, but if I take my ohm meter there is zero resistance to ground from the steering column shaft. So somehow it's finding a ground.

 

[pdentrem]

You really need all three ground straps and more depending on the car. The body sits on rubber mounts even though it is bolted to the frame as the bolts are not directly in contact with the frame, and the engine/tranny usually is on rubber mounts, so body, chassis and engine need grounds.

The steering column will ground via the shaft bearings to the outer jacket which is bolted to the underside of the instrument panel and the firewall. It can also get ground via the shaft itself if there is no rag joint before the steering box. Some cars will have a ground strap to straddle the rag joint to ensure continuity.
Pierre

 

[alloy]

The body has a 8awg ground strap ran to the bellhousing bolt where the ground wire from the battery cable is, and there is another 8awg strap ran to the frame.

But again I don't trust just running a ground of something just to the frame or body. I have ground blocks both front and rear where everything is grounded to except for the steering column which somehow has found its own ground.

I've been thinking that the power took the least path of resistance at the "t" in the ground when i had the horns and fans grounded with the one 10awg wire going to the engine block. And when I separated the fan and horn ground the problem was solved.

I'm sure there is some kind of explanations to this, but I'm not an electrical engineer and probably won't get an answer as to why. But it's fixed and time to move on to the next part of the build.

 

[Jake M]

I'm sure there is some kind of explanations to this, but I'm not an electrical engineer and probably won't get an answer as to why. But it's fixed and time to move on to the next part of the build.

There absolutely is an explanation. With your update you just gave, I can say with confidence that electricity from the horn was going through the fan instead of to ground, because it WAS the path of least resistance. The ground path had more resistance than it should have. Much more. That made it easier for all (or most) of the electricity to go through the fan, doing work, then it was to go through the ground path. The shared ground should have been no problem at all. I can also speculate (without much certainty), that if all you did was to run two separate ground wires to the same junction block (ground block?), that the problem simply a bad splice at that "t" you added to the original, functioning fan ground wire. But if it wasn't the splice, it would have been on that one leg of the "T" that should have provided the low resistance path to ground. So that leg of the splice at the "T", damage inside that chunk of wire, the terminal of that wire at the "ground block", etc. I presume you've now verified that the ground block works, by attaching both grounds to it?

Don't fear electricity or the volt meter. I mean, I'm not saying to just stop everything and be comfortable with that right now, this afternoon... A, it's just not gonna happen, and B, you don't get comfortable with stuff that way. Just stick the volt meter on stuff. Deduce the problem until your're stuck, but note what you found. When you find the problem by other means, the readings, if they didn't make sense the first time, they sure won't the second time. In this case, battery power going into the horns, and (speculating, based on guessing what components you've got and all.... seven or eight volts on the ground pin at the horn. That should have been zero, with a slight (partial volt) maybe for the crazy long ground wire. No math, it's just clearly not got an easy path to ground, as the volts (electrical pressure) is too high for what is (essentially) an open electrical drain pipe.

Seriously. Play with it some. The black magic very quickly goes away. Most of that comes from the fact that electricity is such a very increadibly deep field, that it's overwhelming. You need not take on the whole thing, you don't even need the tip of the iceberg. The water in a pipe (or hose) analogy does 90 percent of what a modern technician does on a modern vehicle. Volts is like pressure. Amps is like flow. And resistance is a restriction, a crushed pipe, or a kinked hose. That's it. That'll pretty much take you through a whole car. No advanced science needed. Just a pressure and flow gauge, but for electricity.