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simple Electrical Question

2K views 34 replies 11 participants last post by  lg1969 
#1 ·
67 Chevelle... with ignition on, test light is bright when testing the positive side of the coil. Test light also goes on when you hit the negative side (ignition is on) as soon as I put the wire that goes to the points on the coil the test light only gives of a a VARY dim light and vehicle will not fire. Any ideas
Thanks in advance
 
#2 ·
Points welded closed or short to ground in the wire or distributor.
 
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#6 ·
What your describing is normal. Engines need air (generally a given), fuel, and a well timed spark to run. What were the sequence of events that led up to your no start condition? Did it just stop, you were doing maintenance, was the distributor out of the engine?
 
#7 ·
What happened is the car was starting very very hard as always does when it gets hot. Would not start. So I let it cool down but this time when it cooled down and tried re start it spun real good but would not fire at all, nothing !! This has never happened when the car has cooled down, even after being in the garage for 10 years until this spring
 
#29 ·
This right here is what leads me to the coil. When hot your coil was breaking down and would not restart until cooled off.

Your voltages on your primary side are a tad low but should fire the engine. Your points are functioning correctly because you are getting a blinking test light on the neg side of the coil.

The secondary side of your coil is not producing the voltage needed to produce a spark. You should retest this to make sure. On your first tests you seemed unsure. Remember you need a small gap between the coil wire and ground to get a spark. Get help, do whatever you need to do to get this test done to your satisfaction.

We can check the coil with this method: https://www.yourmechanic.com/article/how-to-test-a-spark-plug-ignition-coil-by-eduardo-ruelas . BUT, even if the coil checks out and passes, it may not pass when it heats up or is subject to vibration.

You can take your coil to Autozone and they can test it and say it's good, but they can't duplicate the under hood temps that may be causing the hard start conditions in the past. These hard starts may have been the preliminary conditions of complete coil failure you now appear to have. Timing, fuel, and electrical issues can cause hard starting too. We'll get back to those if we get the spark to the plugs as needed.

Since checking the coil to cap wire was mentioned, remove it and set your meter to ohms. Since it is so short it should ohm out below 100 ohms possibly close to 50 depending on which brand and type. If it's much higher or reads 1 (open circuit) on the ohm meter it's bad and needs to be replaced.

From what I see, everything is pointing to the coil. If you buy a new coil, purchase an oil filled coil. They tend to last longer that the epoxy coils.

Now if you're not in the game for originality, I suggest the HEI ignition. https://smile.amazon.com/ACDelco-93...y&sprefix=HEI+,aps,208&sr=8-6#customerReviews Buy the HEI ignition and a set of plug wires for the HEI and the plug to install the HEI. https://smile.amazon.com/Distributo...AQ7KWASDZZ3&psc=1&refRID=05R2B6S3NAQ7KWASDZZ3

The HEI will require a simple rewire that we can talk you through. The distributor swap is easy and there's a few tricks to make it easier. The HEI is one of the most common and reliable ignition systems on the road today.
 
#9 ·
The light will dim if neg side of terminal is connected to the points. The light will be dim because of the resistor wire and the points are closed. The should get brighter went the points are in the open position. During cracking the should stay bright all the time because the resistor wire is bypassed.
 
#11 ·
Do not file them unless you have a point file. You will take off the tungsten point coating and they will burn out and pit very quickly.
 
#13 ·
Well it has been acouple of weeks, put in a new condensor, cleaned up the points and gapped them, put in a high torque starter. tried to start her this morning and nothing. Pulled a plug and grounded it out right to the battery negative. NO SPARK. I am stumped. Coil test is fine. never had this probelm in 40 years. Any help would be appreciated
 
#14 ·
What is the voltage at the + side of the coil with the key on then in the crank positions? Should be at or near battery voltage.
 
#16 ·
Stop grounding your spark plug at the battery negative terminal. The battery produces hydrogen gas, you're looking to Hindenburg your battery if you get the gas and spark at the same time.

I'm thinking coil or condenser if your voltage is good into the coil and your points are gapped properly = proper dwell.

To test you condensor, remove it. Touch the lead to case, hook up an ohm meter. It should start at 0 then build to infinity. If it starts at infinite, closed circuit/shorted out, it's bad and needs to be replaced.

Coils can test good but still be defective. It's usually a temp related failure. As the coil reaches a certain temp the internal resistance builds and no spark.
 

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#20 ·
I'd be willing to bet your coil is good based on your first post. With everything hooked up, crank the engine with the test light on the negative side of the coil and see if it flashes. If it does not flash you won't get spark.
 
#19 ·
After you install your parts see if she goes. If not, test for spark again. Don't use the battery post as a ground.

If you have spark, then remove the air cleaner lid. Look down the carb and move the throttle linkage to full open. Do you see fuel squirting into the carb? If not you're not getting fuel to the carb.

If you see fuel and spark you might need to adjust the timing one way or another to get it started.

If you don't have a volt/ohm meter you should get one. If you don't know how to use it there are plenty of youtube videos to show you. You can also ask here and we'll walk you through it. A cheapy under 15.00 will work fine.

You'll probably want to buy or borrow a timing light. Since you said it was tough to start, your timing maybe off or your battery terminals dirty and need cleaning. Timing lights are a little more costly. You might be able to borrow one from the local auto parts store.
 
#21 ·
OK This is where I am

Checked voltage both sides of coil, ignition on...... 12 volts

Checked both sides crsnking.... 9.6 pos 7 neg

Rotor spinning fine new condensor

Test light flashes on neg. side of coil .. yes
Points closed ignition on ... 4 volts pos <1 volt pos
getting gas, battery is hot...... still no spark.

Really getting depressed over this, I could go 5 years without starting this thing and it always fired right up

Any Thoughts appreciated. PLEASE
 
#22 ·
Check to see if you get spark off of the coil wire to ground when cranking.
 
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#23 ·
When you replaced the starter, did you hook up the yellow wire to the R terminal at the solenoid and to the pos side of the coil. Your cranking voltage is low on the pos side of the coil during cranking.

Actually your coil is getting enough power to produce a spark. Do Levon's test and you should see a spark. If not, coil.
 
#24 ·
Hi hooked up starter properly, this same condition exsisted prior to the new starter. just wenr out and cranked her over grounding out the coil wire, could not see a spark. but it was kind of bright out and by myself but did not appear to have a spark
 
#26 ·
Since the test light flashes on the neg side of the coil when cranked, its probably out of time due to you messing with the points. Dwell affects timing. Loosen the distributor enough to turn it. Run a temporary jumper from the battery+ to the coil+ terminals. Advance the timing a bit while cranking with the key. If the engine starts you'll need to remove the jumper to turn it off.
 
#27 ·
New coil wire?
 
#28 ·
Might want start with an understanding of a points system, not to mention a few minutes of electrical theory.
A coil has a very low DC resistance. It's an inductive device.
The 12V on the primary side, when disconnected, induces a high voltage on the secondary (plug) side. The condenser, actually a capacitor, absorbs and stores the energy from the desire of current to continue to flow when told not to. Or, it stops the arc.
The starter ans ignition aren't very related.

Bottom line is do basic troublshooting.
 
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