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05-13-2023, 12:59 PM | #1 |
Junior Member
Join Date: Jul 2012
Posts: 28
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no power at coil
Hi Guys. I need your help again. I wanted to build up a couple of distributors to carry in my car. I replaced all the parts with modern points and new lower plate with longer wire. The first one I installed worked perfectly, but the second one wouldn't start the car. When checking for voltage, there was power at both sides of the coil but when I turned on the key, there was power on the drivers side of the coil but no power on the passenger side of the coil. What do you think?
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05-13-2023, 02:11 PM | #2 |
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Join Date: May 2010
Location: Largo Florida
Posts: 7,225
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Re: no power at coil
Seems like the primary lead is grounding somewhere. Keep disconnecting from inside distributor back until you find power.
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05-13-2023, 02:44 PM | #3 |
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Join Date: May 2010
Location: Epping N.H.
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Re: no power at coil
Put a piece of paper between the points and see if it still does it.
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05-13-2023, 04:32 PM | #4 |
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Join Date: Jan 2012
Location: Western North Carolina
Posts: 3,946
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Re: no power at coil
If one side is still at zero volts after putting the paper between the points then you have a ground where there shouldn't be one.
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05-13-2023, 04:57 PM | #5 |
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Join Date: Jun 2010
Location: San Antonio, Texas
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Re: no power at coil
Check between the two small terminals with an Ohm meter. It should about 1.5 Ohms give or take a little. If not then it may be damaged. The coil is basically an electromagnet when it is connected to a battery. It won't induct a high tension response unless the ground side it disconnected such as is accomplished by the breaker points. On the car, the points have to be closed to energize the coil. If the points are open, touching a test light to the ground terminal will complete a circuit and the test lamp will light up due to the ground lead on the test light. A coil that is bad with an open in the primary will not function.
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05-13-2023, 07:29 PM | #6 |
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Location: Huntington, NY
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Re: no power at coil
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05-14-2023, 08:36 AM | #7 |
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Join Date: Jun 2010
Location: San Antonio, Texas
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Re: no power at coil
"Short" may not be the best way to describe it. The coil is a load if the circuit is completed to it. It will also overheat if the points don't open and close like they do when the motor is running. Many a coil has died a hard death due to inadvertently leaving the ignition on with the points closed. It also drains the battery in short order.
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05-14-2023, 09:09 AM | #8 |
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Join Date: May 2010
Location: Huntington, NY
Posts: 271
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Re: no power at coil
Rotorwrench, thanks for your followup on my post. I called it a "short" without suggesting that, as such, it could drain the battery and/or "cook the coil" if left unchecked. Good catch!
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05-14-2023, 05:06 PM | #9 |
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Join Date: May 2010
Location: Austin, Texas
Posts: 925
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Re: no power at coil
You did a good job on the 1st distributor. Go back to the 2nd distributor you rebuilt and look closely where the wire coming up from the lower plate is attached to the points. Make sure it is not grounded there.
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05-14-2023, 09:17 PM | #10 |
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Join Date: Apr 2021
Location: Central Illinois
Posts: 499
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Re: no power at coil
chkolar, X2 all above posts. What year is your car? Adding a bit to Bob's post #6, In November of 1929, there was a wiring change made by Ford Motor Co. They moved the source of the black wire that attaches to the - post of the coil from the yellow wire side of the terminal box to the yellow with black stripe side.
This allows the functioning / opening and closing of the ignition points / proper grounding and ungrounding of the points to be reflected on the ammeter as a slight repetitious discharge as the engine is being cranked over to start the car. When at slow idle it will also show up as a negative jiggle in the ammeter needle. Not all A's have this service bulletin applied. If your car is wired, (stock, with Service Bulletin applied) a short / unintended ground, as mentioned in previous posts will show on the ammeter as a small, but steady discharge, approx 4 amp or two marks on the ammeter??? Check your terminal box and make sure the black coil wire is connected to the yellow black stripe side. With the points blocked open with a business card or folded piece of paper, if you see the discharge, something is prematurely grounded between the + post of the coil (red wire) and the blocked open points. You had the distributor out, and you screwed the ign. cable into the side of the distributor. It can be too tight and cause the buss bar to contact the casting, etc. 2.5 or maybe 3 turns is usually enough. If the cable is old the spring loaded end may be too stiff and stuck, or stuck shy of the buss bar (under the lower plate) and thus is an open circuit and not visible on the ammeter (no discharge). Report back on your findings. There are common ways to bypass the switch and the ignition cable etc. and / or work backwards from the blocked open points arm with the VOM as suggested in post #2, connection by connection to isolate the fault. Good luck.
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"It ain't what you know for certain that gets ya in trouble. It's what ya know for certain that just ain't so!" Last edited by Rob Doe; 05-15-2023 at 03:17 AM. |
05-15-2023, 10:12 AM | #11 |
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Re: no power at coil
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05-17-2023, 08:30 AM | #12 |
Junior Member
Join Date: Jul 2012
Posts: 28
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Re: no power at coil
I discovered that since I was using modern points, the condenser was located on top of the upper plate and the tab used for the original condenser on the lower plate was not being used. The unused tab was touching the distributor housing causing a short. I bent the tab so that it was not contacting the housing and everything work out beautifully. Thanks to all of you that responded.
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