Shock me shock me shock me

[chrismoore701]

Finishing up my painless wire harness on my 79 c10. Driver side headlight assembly grounded to the fender. Passenger side grounded to the frame. Cab and engine grounded to the frame. Battery grounded to engine. When I honk the horn I get a small shock if I am touching the fender. Thoughts?

[chrismoore701]

I am guessing I need to dress my grounds a little better. Cab and engine to the frame I do not have the star lock washers on

[Eyegore]

So I guess it's not really "painless wiring"!

Sorry I could not resist.

I believe your on the right track, it has to be the ground.

[mongocanfly]

Hehehehe...I guess now its painful wiring....

[chrismoore701]

you guys are funny
Shocks are not too bad, but my wife sure got a kick out of it

[chrismoore701]

Question is, can you name the movie the shock me quote is from?

[ray_mcavoy]

Getting a small shock from the horn is normal if you have a metal horn button.

When the horn relay is energized, it builds up a magnetic field in the relay's coil that pulls the relay contacts closed to power the horn. When you release the button it opens the circuit and that magnetic field collapses, inducing a voltage in the coil. Basically the same concept as an ignition coil. So you can get a shock from the inductive kickback if you have an un-insulated horn button.

The fix would be to install either an insulated horn button or a diode across the horn relay coil.

[chrismoore701]

I have not installed the button cover on the steering wheel. I was just pushing the metal ring. That helps

Thanks

[slotard]

I'm awfully surprised that a 12v system provides enough of a shock to notice.

[ray_mcavoy]

Originally Posted by slotard

I'm awfully surprised that a 12v system provides enough of a shock to notice.

The voltage in this case is being generated by the collapsing magnetic field inducing a voltage in the relay coil. Depending on the current that was flowing through the coil prior to the circuit opening and the number of turns of wire in the coil, the voltage can be quite high.

Ignition coils are specifically designed to take advantage of this by having a secondary coil with a large number of turns in comparison to the primary. They're capable of generating thousands of volts even though the primary is only 12V (or less in some cases with a ballast resistor).

Here's a good description --> http://www.douglaskrantz.com/ElecFlybackDiode.html

[snaptoo]

I agree with the relay / coil theory and believe me you can get "whacked" darn hard with 12 V if you are grounded ! Like trying to jump start a ski boat while being in the water !

[chrismoore701]

Just a little shock, just enough to notice, not like a spark plug. but I should get my kids out there to try and see what they say, could be fun to watch

[slotard]

Yeah but you can grab both battery terminals and feel nothing

[wilkin250r]

And a lot of times it's difficult for us electrical-minded people to explain issues to non-electrical, not because you're dumb, but simply because it's another language. If you don't know Amps and Watts and Coils and Capacitance and Induced voltages due to collapsing magnetic fields, how else can I explain it? I don't have another word for "volts", I don't have a clever analogy. It's "Volts", that's what it's called, that's the only word I have for it.

So, you guys are correct, 12V by itself is not enough to give you a shock on dry skin, or even wet skin (but don't touch your tongue to it!). If you are getting a shock from a 12V system, it HAS to be boosted some way, and apparently it's the Horn Relay (and thank you to Ray. I'm an Electrical Engineer, but I don't know this circuit, so I had no idea where it would come from).