Electrical shock question

[sweezy722]

My motor started to run a little rough like an occasional miss. I then noticed the tach going all over the place. I though I may have a wire loose and reached my hand under the dash to feel. I guess I touched the back of the tach and it fried my left arm. We are talking about the full 40,000 volts. That was 6 days ago and there are still 3 spots on my arm. I have a new respect for the tach wire. Last year I remember touching the back of the ignition key while looking at the fire extinguisher and getting a small tingle but nothing like last week.

Any thoughts or ideas? Is this normal or just a loose wire? Is the rectifier bad?

Thanks for any help or ideas.

 

[mrwiggles2]

Re: Electrical shock question

My tach was off and on working, seemed if you wiggled the wires behind it, sometimes it would work. I never got a shock. I fixed the problem last weekend, corroded terminals was the reason.

Maybe someone else can offer help but I wouldn't think you would get that kind of power to a tach. I would hook up a multimeter to your rectifier and see if it is working.

 

[john from md]

Re: Electrical shock question

Your tach signal is AC voltage. It will shock you just like house current. The small tingle you got was when you probably touched 12 wires with sweat on your skin.

If you get complacent around electricity, we will be reading about you in the paper.

John

 

[Showtime22]

Re: Electrical shock question

If the motor was changing RPM's and running rough, I'd think the Tach is showing what is happening to the motor.

However my tach wires to the coil and I'd guess a short circuit could affect the coil.

Try disconnecting the tach when the engine is off and see if the engine still runs rough.

 

[Frank Acampora]

Re: Electrical shock question

The tach has two power sources going to it: 12 volt power to run the electronics and 16-18 volt power coming from the alternator. Since the 12 volt power source is also obtained from the battery which is being charged at 16-18 volts, it is at the same potential. 16-18 volts will give you a tingle, especially if your hands are damp and/or you are grounded.

 

[sweezy722]

Re: Electrical shock question

Last week - 6 days ago - I got more than a tingle. I have 3 burn marks on my arm that are scabbed over. After it happened I also had the start of blood blisters on my arm. I live and work around livestock and it was much stronger than any electric fence I have ever come in contact with. This is the strongest shock I have ever got anywhere.

I did not find any loose wires. I am wondering if my bouncing tach may be shorting out and feeding AC current over. Is this possible or am I totally off base.

 

[Frank Acampora]

Re: Electrical shock question

High amperage at low voltages will burn just as well as high voltage.

HOWEVER: The ignition system is charged by dedicated separate coils on the alternator and these windings produce approximately 250 volts AC to charge the ignition capacitors. Is it possible that your tach is getting this current from a short or improper wiring?

If your tach is wired to get signal from the coil terminals, then it will definitely be getting 250 volts. And that is a lot stronger than a cattle prod.