Our friend Ralph always called it a disturbutor, and in this case so do I. I loathe, despise, and abhor intermittent electrical problems, and this is one of those. Sometimes the truck starts right up with no problem, and sometimes there's no spark, like today. My electrical knowledge is rudimentary, so I thought I'd better check and see if I understand this correctly.
A test light shows current coming from the switch.
It shows no current coming from the other terminal. I believe the circuit is supposed to be from the switch to the first terminal, through the primary coil winding and out the second terminal, and through the points to ground.
Before I go plunk down my dough, I want to be sure the lack of current from the second terminal indicates the coil is intermittent or bad.
You are correct, I see a new coil in your future.
If the points are closed light will not light up.
If the points are closed you won't get a light when testing at the point terminal on the coil. That's #1. #2, unless you have a positive ground system, (and you might looking at the pics I'm assuming you're dealing with some more antique iron) the coil is hooked up backwards. + it power in - goes to the point wire. Just in the dark guessing I agree with Mark. Your coil might be going bad. It could also be a bad condenser.
Steve, before you replace the coil swap out the condenser. The ones they make these days have the life expectancy of a mayfly and a new one will cost a small fraction of a new coil. Also, they're famous for being intermittent.
well, Dodges are typically positive ground, AND you won't get a light if the probe is on top of paint, which acts like an insulator!
The others are correct, if the points are closed they will complete the circuit to ground instead of your test light, my mistake. Pull off the distributor cap and stick a thin piece of cardboard between the points, then repeat your test.
Another check you can do at the same time is pull the cable off the center terminal of the distributor and place it near a ground. When you pull your test light away from ground, the coil should fire and you should see a nice blue spark from the end of the coil wire to ground.
Let us know how it goes!
I dont think you will get power there with closed points. why not take off cap and open and close points with screw driver and see if you get spark? its probly bad points. what is it a dodge?
That looks suspicously like the engine in this car
So I went outside and checked mine I do get voltage on both sides with the points closed. Remember positive ground unless it has been modified.
Checkout the diagram below, its simplified and doesn't show the capacitor, but its all you need to diagnose.
If you have voltage on the + terminal of the coil (light on) the ignition part of the circuit is OK.
The negative terminal of the coil should be light on if the points are open and light off if they're closed. (turn the engine over or use your fingers or insulated screwdriver to open and close points)
If the light is always on when connected to the negative terminal of the coil, the points aren't closing, are bad or the wire from the coil to the points is broken or open.
If the light is always off when connected to the negative terminal of the coil it can only be due to a bad primary winding in the coil or the wire to the points is shorted where it passes through the distributor body (assuming you have voltage to the positive terminal).
But he's getting power to one side of the coil. If the points were closed and therefore, the circuit grounded, there wouldn't be power to either side, would there?
If his tester doesn't light up when connected between ground and the negative (or points) side of the coil, do this test. Disconnect the wire at the negative post on the coil (the one going to the distributor). If the light now lights up (when connected to the negative post and the ignition on) the coil is probably good. If not, the coil is certainly bad.
With that wire reconnected and the points held open with a piece of paper, if the light is off, there is a short in the wire going to the points. (I didn't show it in the diagram but the capacitor is connected directly across the points, if its shorted, it will short the distributor wire to ground also - disconnect it to be sure).
One other thing to check,the negative coil wire sometimes shorts where it passes through the distributor body. I have seen this on several cars that wouldn't start.
There would be power, but a test lamp is not the way to determine that, as electricity goes the direction of least resistance, and a good ground would have less resistance than the test probe lamp. A volt meter is needed here. An intermittent problem like this is usually a bad distributor wire inside the distributor--it can break inside the insulation and make a "Lucas connection" (ie: sometimes it's there, sometimes its not). If you disconnect the coil end of the wire, put an ohm meter on it, and advance/retard the distributor (pull on the vacuum advance) the ohm meter reading will change if it's the wire (and maybe not, if you're unlucky!).
Of course, other causes can be a failing condenser, dirt on the points, AND a bad coil! Bad coils usually show up when they are warm though--fire up fine cold, and then fail when warm. USUALLY! We are talking electricity here!
PS, the diagram in Bud's post assumes negative ground, reverse the + & - signs for positive ground.
Steve, any update, or are you working on one of your many other projects today?
Oops double checked I get power on the points side of the coil with the points open.
You SHOULD get power on both sides of the coil if the points are open. There should be no light on your tester on the side of the coil going to the points if the points are closed.
With the points closed you are effectively shorting the distributor side of the coil to ground - hence, no light.
BTW A simple distributor system (not CDI or electronic) is a low impedance DC circuit - a test light will diagnose just fine.
It IS possible for the coil secondary (high voltage side) to fail open. A test light won't help here. This is less common then problems on the primary side.
I was busy with other stuff for a few days, but got back to the Dodge this morning. As the picture shows, there was current all the way to the points.
I checked the gap and found it over .030", so I filed the points and reset to .020" as the book says. When I pulled the starter lever here's what happened: https://youtu.be/zFvcpRmdpSo
In fact, before I made the video I stuck a screwdriver in the #1 plug wire and held it near the plug to see if it would show a spark. When I pulled the lever it started instantly and ran on five cylinders. Now I'm ready to haul away yard waste and construction scraps. Thanks to all who helped me get back in operation.
Great news! Glad you didn't have to spring for a new coil. You probably already know that changing your point gap changed the dwell, which changed the timing. Since it's a work truck, you may not care as long as it runs.
Is the choke hooked up and working? From one of your earlier yard work videos it looked like the truck kept stalling when you engaged the clutch.
Yep, the choke works. Those stalls were on a cold start. After it warms up a little, no such problem.