• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR4/4A Getting electrical shock from horn button when using the horn.

Share this page

J

jimmyr

Senior Member
Country flag
Offline
New owner of aTR-4A, and am getting a kick back electrical shock when pressing the horn button. Have tried adding a diode to one of the horn relay terminals, but no luck quenching the the problem.
 
I would have been fairly sure that, absent conduction directly thru an opening in the skin, it would not be possible to feel a shock from a 12 volt dc source.
Bob
 
The diode should be on across he relay coil. You could even put one across the horn switch. Be sure to put in the correct polarity.
 
Correct, I must have put the diode on the horn side of the relay as the terminals are not marked. I will move it over to that terminal. The car is a negative ground system. BTW, the inductive kickback from a coil equates to several hundred volts thus the shock conditions.
 
12v DC will not give an electrical shock; the voltage is too low. It will burn you from the heat of high amperage and make your wires and skin smoke. One must always keep the smoke inside the wires. Perhaps you are actually feeling heat and confusing that for a shock. So let the device honk. If it does not honk, it will burn you or blow a fuse or catch fire.
steve
 
All fixed, I moved the diode to the relay coil wire that goes to the horn button. The horn button on the Moto steering wheel is metal, so you are in contact with the relay winding and the inductive kick back that measured 300V on my VOM - so this pulse was felt.
 
Ah - metal button. Thanks for the clarification - and happy you resolved the issue! (A horn is supposed to "jolt" other drivers to attention... not yourself!!!)
 
I had that problem on my TR4a, especially one of my bare arm was resting on the metal window ledge.

I was living in Fort Walton Beach Florida, humid out there.

Lots of surface area for conduction through your skin. And the horn button was metal.
 
Interesting. I would have thought that the horn inductance wouldn't be high enough to cause this, but obviously it is. I didn't know that TR4s once had metal buttons; mine is plastic. I'm surprised the factor did that; it's really asking for trouble.
 
Back
Top