Horn shocks!

O

ojxxx

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When pushing the horn and touching the spokes on the steering wheel you get a shock.
I've eliminated all but the concrete the car sits on, I changed coil, distributor, plug wires, horns and horn relay and now I have it to the point where I pulled the harness loose and have the brown wire from the fuse going to the coil of an idecube relay and connect the wire from the steering column and the little shit will give you a tingle when calling for horn and touching the steering wheel spokes at the same time.
I don't get it, this is 12v we are dealing with. I thought it had to be some ignition bleedover and thats why I changed all that stuff.
Any ideas?
Thanks, Oj
 
Probably a Bad Ground

The horn switch completes the ground. Power first goes to the horn and then to the switch. When you push on the horn ring, it closes the switch and the power goes to ground. Check the wiring to make sure the ground side of the horn switch is well grounded. If you are getting shocked, there may also be a problem in the wire to or from the switch, and the juice is going to ground (obviously) through you.

Do you get shocked when car is not running?

Good luck!
 
HolyCat said:
The horn switch completes the ground. Power first goes to the horn and then to the switch. When you push on the horn ring, it closes the switch and the power goes to ground. Check the wiring to make sure the ground side of the horn switch is well grounded. If you are getting shocked, there may also be a problem in the wire to or from the switch, and the juice is going to ground (obviously) through you.

Do you get shocked when car is not running?

Good luck!
Click to expand...

Yes, it'll shock you with key 'OFF' and coil totally disconnected. The ohms resistance from steering wheel spoke to the horn relay ground terminal is .1ohm measured with Fluke87; from steering wheel to engine it read .6ohm so I think the reading is right.
 
A Few Questions

Oj,

In your posts, you mention a horn relay. To what are you referring? I am not aware of a relay (a low-amp switch that operates a higher amp switch) as part of the stock horn system. Attached is a wiring diagram for a Mk 1A Tiger. I believe the horn wiring system is identical for Mk 1 and Mk II Tigers.


Horn Electrical System
The wire from the battery connects to a spade (No. 3 on diagram) on the back of the ignition switch. On that some spade is a brown wire that goes to a terminal (No. 1 on diagram) on the fuse box. This is unswitched. On the other side of the fuse (No. 2 on diagram) for that terminal are two purple wires, each one going to one of the horns. (One of those wires has a "take off" going to the map light and the other wire has a take off for the interior lights for GT models.) Coming off each horn is a purple with black stripe wire going to the horn (push) switch, which is a slip ring. When you push the horn ring, it closes this switch and the amps can then go to ground.

If you are getting shocked by touching the steering wheel spokes while pushing on the horn ring, it sounds like the 12v at the horn switch is not able to go to ground through its ground wire when you push on the ring, and is instead finding a ground through the horn ring to you, then to the steering wheel spokes, and then to the steering column. You might want to check the resistance from the horn switch to another ground point. I suspect that the ground connection on the wire from the horn switch is not good for some reason. Have you tried disconnecting the horn switch ground wire from the ground, clean the terminal on the wire and whatever is the ground point, and see what happens?

The other possibility is that the horn switch slip ring is not completing the circuit when you push.

What is perplexing is that I did not think the horn ring got "hot" when one pushes on the ring to sound the horn, but it has been awhile since I looked the horn slip ring and how things were connected. I always thought the horn just would not sound if there was a problem with completing the circuit to ground when pushing on the horn ring.

I do recall that there is a big, fat screw on the underside of the clam shell steering wheel column cover. If one is not careful when reassembling this, that screw can go into one of the wires for the horns or turn signals. You might want to check that as well.

Good luck!
 

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You are right, the original did not have a horn relay. When I wired the car there was a horn relay added to the left side, both horns were mounted there. I replaced the old horn relay and wired the ground coming from the horn ring to the ground of the relay and broke the 12v horn supply thru the relay. During a subsequent conversation with the owner I learned that he had added the horn relay for an electric radiator fan, a fan that was not on the car when we received it for building.
The turnsignal mechanism casting was broken, no replacements are available. I found a similar casting and machined it to work the turn signals, the horn ring contact arm would not work with this piece so I made a new mountings for it and polished the contact points. The actual contact felt firm and positive, I didn't take ohm readings, I'm sure it was zero. But I do know what you are thinking. It seems the problem must be right there. I am looking at making jumpers to bridge the universal joints, I'll be doing that this morning.
 
That did it! I made an electrical jumper to go around the lower universal joint at the R&P and it cleared it right up! WooHoo!
 
I have

The same problem but have been wondering as it only happens when road rage is creeping up on me ;-)
Thanks for asking this question.
 
You Found the Problem!

ojxxx said:
That did it! I made an electrical jumper to go around the lower universal joint at the R&P and it cleared it right up! WooHoo!
Click to expand...

Great - you found the problem. With the jumper wire, the horn contact plate and striker on your car seems to be going to ground through your steering column, to the rack and pinion, and then the chassis. I am not sure, but I thought the turn signal is clamped to the upper part of the steering column with metal to metal contact. The turn signal assembly has its own wiring loom, containing six wires. I wonder if one of those wires goes to ground. If so, maybe your fabricated turn signal assembly lacks that ground wire (if there is one - I don't know) and/or metal-to-metal contact for the steering column.

The wiring diagram shows the ground for the horn switch to be by contact. (The diagram uses the term "via fixing bolts." It does not show a wire ground for it.)

In any case, you might consider some sort of ground wire on the steering column outer tube (the part that is fixed) instead of relying on a jumper around a steering column u-joint. Should be an easy fix.
 
I am an old school electicial techo. I worked with 50VDC in telephone exchanges for many years. The telephone exchanges also had 70VAC for ringing the phones. Only the AC current every gave a shock. The 50VDC never.
So I fail to know how a 12VDC horn circuit could give a shock.

There must be another AC circuit for a shock.
 
steven said:
I am an old school electicial techo. I worked with 50VDC in telephone exchanges for many years. The telephone exchanges also had 70VAC for ringing the phones. Only the AC current every gave a shock. The 50VDC never.
So I fail to know how a 12VDC horn circuit could give a shock.

There must be another AC circuit for a shock.
Click to expand...

I agree and know what you're saying. But take this as fact, the only load on the system was the coil of a relay and the battery was the only source of power. In testing I had the harness laying on the fender with an 'icecube' relay connected without anything else connected, the ign key was 'OFF', nothing else in the car was working. I believe the coil for the relay draws 60 milliamps, thas all the current it was drawing.
I just can't understand how 12vdc would shock you like that, but it did.
 
New
The shock is back! I'm ready to call an exorcist! The shock returned when I put the pertronix coil back in it, earlier in the thread I said I replaced the Pertronix coil with a Mallory and it made a big difference, well I thought it couldn't have made any difference because it isn't running and the ignition is 'OFF' the coil can't make a difference! Well, I put the cars' ignition back to Pertronix distributor and coil (matched set from Pertronix) and now the shock is back (not as severe, just a mild tingle)! With the key sitting on the dash, the car not running, no power to the coil you hit the horn and you'll get a shock!
Here's what I did this time, the battery is in the trunk and the ground point is in the rear. I ran a temporary #2 cable from the battery post and clamped it to the altenator bracket with vise grips and the shock is gone, again.
I'll need to run a heavy gauge cable from the battery ground point in the rear to something up in the engine bay, then use some flexible jumpers to proper ground the engine etc.
There must be some kind of short/bleed in that coil and its' affecting the ground somehow.
Anybody have any other explanation? I'm open to anything at this point!
 
Engine Ground Cable?

Have you checked your ground cable from the engine to the frame? I know it is pretty obvious, but perhaps one of the connections is loose or has had corrosion build up.

Having suggested that, it still does not make sense. There should be a good ground between the steering column and the frame and you should have a good ground between the horns and the frame.

I don't know if it would help, but you might check to see if you have voltage at the horn ring (measured by sticking the pointed probe into the backside of the outer ring) without trying to sound the horns, and then while pushing on the ring to sound the horn. If there is a difference in voltage, I don't understand how pushing the horn ring would make a difference.

Also, did you measure the resistance from the steering column to an instrument ground under the dash?

Good luck (again).
 
HolyCat said:
The horn switch completes the ground. Power first goes to the horn and then to the switch. When you push on the horn ring, it closes the switch and the power goes to ground. Check the wiring to make sure the ground side of the horn switch is well grounded. If you are getting shocked, there may also be a problem in the wire to or from the switch, and the juice is going to ground (obviously) through you.

Do you get shocked when car is not running?

Good luck!
Click to expand...

Yes, all of this happens with the Ign in the 'OFF' position. Car is not running.
 
ojxxx said:
Yes, all of this happens with the Ign in the 'OFF' position. Car is not running.
Click to expand...

It is because the horn coils or the relay coil is a reasonably big inductor, and (due to a wiring or assembly error) the circuit for the horn (relay) is electrically connected to the horn ring. When you let off the horn ring, the circuit is broken, but the inductor tries to keep the current going, and this results in a high voltage spike in that circuit. If you are touching any part of that circuit, you will feel a shock.

I know this, because I've done it myself... ended up reassembling the steering wheel center with some nylon insulators and fixed the issue.
 
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