thanks to all for you future patience. happy memorial day
Full Version: electical testing 101
this is real beginners stuff, but i am electrically challenged. i am trying to measure the voltage at coil looking for 12v on the pos and 0 to 12v as the points open and close (for those who have been following my progress, or the lack of thereof) the petronix is history, but i digress, so how is this done. to test the pos do i set the meter to 20 dc, attach red lead to pos on the coil and black lead to ground? and to test the neg is it red lead to neg on the coil and black lead to ground.
thanks to all for you future patience. happy memorial day
thanks to all for you future patience. happy memorial day
Yes
QUOTE(SLITS @ May 24 2009, 07:51 PM) 
Yes
No. 1st part correct. two choices to check ground. You can use the res. setting and check - to ground, or +12 to neg. on 20VDC setting. Keep in mind if you put the red on the + side of the coil, and black on the - side of the coil, you ould need to turn the dizzy by hand slowly to see voltage on any low end digital meter. They just are not fast enough to pick it up. A old dial (analog) meter will pick it up. For newbies, radio shack has a book on how to use multimeters. It's quite good.
QUOTE(underthetire @ May 24 2009, 06:59 PM)
QUOTE(SLITS @ May 24 2009, 07:51 PM)
Yes
No. 1st part correct. two choices to check ground. You can use the res. setting and check - to ground, or +12 to neg. on 20VDC setting. Keep in mind if you put the red on the + side of the coil, and black on the - side of the coil, you ould need to turn the dizzy by hand slowly to see voltage on any low end digital meter. They just are not fast enough to pick it up. A old dial (analog) meter will pick it up. For newbies, radio shack has a book on how to use multimeters. It's quite good.
sorry guys still not getting it.when i test i get 10.3v testing pos and 0 when testing neg, while cranking the engine. what is the res setting you mentionrd.?
With the key on .... you should get voltage at the + side of the coil (actually, it's the wire coming from the relay board that is energized).
The distributor acts as a ground to complete the circuit from the coil. When the points are closed, juice is flowing, feeding the primary(?) winding in the coil which is inducing a charge in the secondary(?) winding of the coil to saturation.
When the points open, the ground is lost and the field collapses in the coil, producing the spark to the dizzy cap to be distributed to the spark plugs.
You would have to place the VOM in series with the green wire from the points to read any voltage thru the points. Otherwise, with the points closed, you would set the VOM to ohms to check for continuity. Red lead to green wire (disconnected from coil) and black lead to ground.
I don't check for anything on the - side of the coil, but I'm pretty sure that's how it would work.
In lieu of what I wrote .... read this Coil / point function
The distributor acts as a ground to complete the circuit from the coil. When the points are closed, juice is flowing, feeding the primary(?) winding in the coil which is inducing a charge in the secondary(?) winding of the coil to saturation.
When the points open, the ground is lost and the field collapses in the coil, producing the spark to the dizzy cap to be distributed to the spark plugs.
You would have to place the VOM in series with the green wire from the points to read any voltage thru the points. Otherwise, with the points closed, you would set the VOM to ohms to check for continuity. Red lead to green wire (disconnected from coil) and black lead to ground.
I don't check for anything on the - side of the coil, but I'm pretty sure that's how it would work.
In lieu of what I wrote .... read this Coil / point function
When measuring electricity in a car, remember that you need to measure from positive to negative and the car body is the negative or ground.
This means that when you want to measure voltage at some point with a VOM, you touch the negative (black) probe to the body( a bolt screwed into a body, a bare point in the body or the negative post of the battery) and the positive probe (red) goes to the item you want to measure. I prefer to use the body and not the negative post because when you do, you are adding the the battery ground attachment to the body to see if it's any good. That's red and black as above IF the colored probes are plugged into the VOM correctly- red to positive and black to ground.
With the ignition on or cranking, you should mesure 12 v between the + side of the coil and the body of the car. To measure across the other side of the coil, touch the positive probe to the point where the distributor wire connects to the coil and connect the negative post to ground. When you crank the engine, the VOM should measure a pulsing 12 volts. Now here is where it gets a little tricky. If the VOM has a needle indicator, the needle should swing from side to side in response to the pulsing 12v.
If the VOM has a digital indicator, it apparently craps out as the digital circuit in the VOM just can't keep up with the pulses. It it tries to count the display up and down but the pulses come too fast and it gets confused. I know because I just checked it on my garden tractor. Thats two things that suck digitally- music and VOM's measuring pulses.
Do you have a test light? They look like a screwdriver with a sharp point instead of a blade and have a wire and clip coming out of the top of the handle? Great test tool, it can respond to the pulsing by flashing a light, or you can use it to test circuits to see if voltage is delivered (lights up).
You should measure 12 volts across the battery and a drop to 9-10v when cranking and measure 14v when you finally get it runing (charging the battery ya know)
Remember that Pertronix are fragile and crap out if you leave the ignition on too long without starting.....
Hope this helps
Ken
This means that when you want to measure voltage at some point with a VOM, you touch the negative (black) probe to the body( a bolt screwed into a body, a bare point in the body or the negative post of the battery) and the positive probe (red) goes to the item you want to measure. I prefer to use the body and not the negative post because when you do, you are adding the the battery ground attachment to the body to see if it's any good. That's red and black as above IF the colored probes are plugged into the VOM correctly- red to positive and black to ground.
With the ignition on or cranking, you should mesure 12 v between the + side of the coil and the body of the car. To measure across the other side of the coil, touch the positive probe to the point where the distributor wire connects to the coil and connect the negative post to ground. When you crank the engine, the VOM should measure a pulsing 12 volts. Now here is where it gets a little tricky. If the VOM has a needle indicator, the needle should swing from side to side in response to the pulsing 12v.
If the VOM has a digital indicator, it apparently craps out as the digital circuit in the VOM just can't keep up with the pulses. It it tries to count the display up and down but the pulses come too fast and it gets confused. I know because I just checked it on my garden tractor. Thats two things that suck digitally- music and VOM's measuring pulses.
Do you have a test light? They look like a screwdriver with a sharp point instead of a blade and have a wire and clip coming out of the top of the handle? Great test tool, it can respond to the pulsing by flashing a light, or you can use it to test circuits to see if voltage is delivered (lights up).
You should measure 12 volts across the battery and a drop to 9-10v when cranking and measure 14v when you finally get it runing (charging the battery ya know)
Remember that Pertronix are fragile and crap out if you leave the ignition on too long without starting.....
Hope this helps
Ken
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